I think they are a bit hard to find, but 3T a while back came out with a 9-32 cassette in two different configurations. If you could get your hands on an XDR Driver, this might be an option. The 9-tooth cog would allow you to drop down the chainring size, which could help bring the 32-tooth cog closer to your reduced front chainring.
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You can get them for half price at Merlin Cycles in the UK:
Mike
Well I tested it today, albeit only briefly (life stuff got in the way).
It’s very quick, comfier than I expected and I was quite happy up a couple of moderate hills without needing to go to the 36, much less need more. But the gearing was a bit gappy, with a gap falling right around what felt like sweetspot on a flat road 
And the seatpost dropped a couple of mm during the ride.
Hmm. Hopefully out for 2-3 hours tomorrow to finalise one way or the other.
If you go for a smaller chain ring, you will push the gap to slower speeds. For example, if you replace the 50-tooth chainring by a 46-tooth chainring, you will push all gears down by one gear (50:12 = 46:11, etc.) and you will get roughly the same gearing as a Shimano 11-32 cassette. If you choose 44- or 42-tooth chainrings you will shift everything by 1.5 and 2 gears respectively.
I have the same groupset on my Allez. I use 46x11-32 during winter and 50x11-28 for crits. 46x11 is adequate and 46x32 is still a bit high for Z2 rides, but 11-32 is about as gappy as I can tolerate on a road bike.
Range, close ratios, simplicity of 1x – pick two.
The magic ratio only works with 50/34 chainrings.
And for sure they won’t work on 1x 
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I’ve spent a lot of time considering 1x gearing options myself (on a commuter/gravel/rail trail bike), using the gear-calculator.com website (very useful)
Initially, when selecting a cassette, I made the mistake of trying to apply experience and preferences from 20 years of riding road bikes with a front derailleur (2x setups), but the reality is that 1x drivetrains are “different” and therefore what you want in a cassette is likely to be different to what you may otherwise prefer or be used to.
By way of example, while on a 2x bike you might want tight gaps in the top (small) gears, with gaps getting progressively wider as cogs get bigger. On a 1x bike your gear jumps need to be considered around a “starting” or “default” gear which should be the middle cog (as this is the most optimal chainline). On an 11s system, that’s the 6th cog with 5 either side.
Then consider the gear you’d be in most of the time on your road bike… at a cadence and speed you just naturally “settle into” when riding solo. We all have a gear like that… and it’ll vary depending on the person! Then look for a cassette and chainring combo that puts you there on that magic middle cog with plenty of room up and down from that starting point.
TLDR; The Shimano HG700 or HG800 11-34 are the best I’ve been able to find and I’d imagine are an excellent starting point for most people. The 21t cog is smack-bang in the middle (6th position) and you have very nice 2t jumps for the three cogs either side of it. That’s 7 gears that are nicely spaced and clustered around where you are likely to want to be. On the low end (easy gear) the teeth jumps then widen slightly, increasing by 3t then 4t (which makes sense, as speed slows and gradient increases). While the high end (hard gear) the teeth jumps remain at 2t but that’s ok because at that end of the cassette the difficulty increases exponentially with each tooth difference (which makes sense, as speed increases and gradient decreases).
11-13-15-17-19-21-23-25-27-30-34
I’ve loved the setup above (with a 40t chainring) way more than I thought I would. Whereas in the past I’d poo-poo’d 1x on the road, if a manufacturer got a 1x13 setup right (adhering the the principles above), I’d probably be done with a front derailleur on my road bike too. I’d simply add a 12t and a 38 (or 39t) to the above.
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I’ll be interested to see how the rumored Campy 1x13 gravel grouppo turns out.
As a campy guy, I totally agree! I hope they nail it. A little disappointed with the rumoured 9t cog though. There’s no reason to go lower than 11t - just increase the size of the chainring.
With gravel tire widths, clearance at the chainstay/chainring can be an issue. Wide chainstays may require a smaller chainring, which in turn may force a 10t/9t cassette. I get that there are frictional losses with 9t/10t, but the amount of time spent actively pedalling in these gears must be pretty small. Damn you, gravel trade-offs. [shakes fist]
Although if you could swap in a larger chainring/cassette 1x13 combo on a road frame (where you aren’t pushing clearance), that could be very interesting.
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You don’t need to wait for Campag to add another cog, you can order a 13-speed drivetrain now on Rotor’s website. For most road riding their 10-39 cassette should cover most needs. Their gearing is identical to SRAM’s 10-33 cassette, with a 39-tooth cog added on top of it.
If you want tighter gaps and don’t need the range, they have a 10-36 cassette, too.
A smaller cog has a much bigger impact on gear ratios than changes in front chainring.
A 4t jump in chainring size at the front is vastly different to a 4t change at the cassette.
This is true… (I’m not sure what you’re trying to point out here…?)
The thing is - you’re not just in a less efficient gear when your in the 9 or 10 tooth sprockets - you’re in a less efficient gear all of the time since the chainring is smaller and therefor, to be in the same gear, the sprocket must be smaller too in comparison to a setup with the larger sprokets and associated larger chainring.
Mike
Well, I reluctantly decided not to go ahead - it wasn’t quite right for me, and it’s money I hadn’t budgeted for, with more needed to get it as I want. That said, it’s opened my eyes a bit to 2 possible projects as time and funds allow: converting my winter hack/commuter to a 1x system (on a budget), and an aero bike, which is something I’d always scoffed at before. I take it back.
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IMHO this argument will be moot as soon as Shimano releases 12-speed groupsets for the road. I’d be really surprised if they did not make the same move as on the mountain bike side.
As a non-mountain biker, what do you mean?
For a winter/commute bike, 1x is a great idea. Less maintenance items.
Aero bikes are always a great idea. All else being equal, why would you not want a more aero bike?
I’m without an aero bike now, but sometimes, it just feels right to throw your leg over a round-tube bike. That still doesn’t stop my aero envy when I ride with buddies on Stradas and their aero ilk.