Why shouldn’t that be possible? Such bikes have been on the market for years at this point, albeit mostly with endurance bike geometry.
You can even go for wider differences in tire size if you are ok with 650b wheels (i. e. the original concept of the Open UP and 3T Exploro). You probably want to stick to a narrower tire width range (hence, tire radius range) if you want to stick to 700c wheels.
The modern riding position dictated the taller stack height. Backs are as flat and bodies are looking aggressive as ever, but resting your forearms on your table-top wide aero bars meant that stack heights had to come up.
You are describing pretty much the geo of my custom bike I have! It is built to be optimal for 700x35 wheel/tire setup. It has road geometry (72.5 HTA with 50mm rake) , and has clearance for 700x42 and 650x50 AND has 408mm chainstays. The 74.5 STA helps keep it nice and aggressive too. It was also built around 165mm cranks.
As they said in the old forum days, your post is worthless without pictures! 
Where did you get the custom frame made?
If you can budget a Foil RC I’d think the Colnago is not out of reach with some additional time to save up for it. That said the Foil is a very fast bike and out in the wind my gut feeling is it will be more efficient than the Cannondale. The current rage of quiver killer bikes seems like so much marketing BS from my own point of view. Shallower tubes regardless of shape will not be more aero than the deeper shaped tubing of a full aero bike. Only speaking of my own experience my round tube bikes are not as fast terminally as my aero bikes. There is much crossover but at the ends of the envelope an aero bike is just faster much like deeper wheels will be faster than shallower ones. I know there is all this data to show that a new Madone or SL8 is faster but it is not really plausible.
Seems like a lot of the time the claims that an all rounder bike is as or more aero than it’s aerobike predecessor turn out to be due to faster specced wheels and/or handlebars and not the frame itself.
So true, and it seems that’s where some of the marketing comes into play. The bike company gets a lower overall drag figure then goes on to proclaim how much faster the bike is than the model before it.
Funny you mention this, my final candidates for a new bike is;
Scott Foil RC
Cannondale Systemsix (not super)
SL8
Winspace T1550 Gen 2
These bikes more or less can all fit into the category of what will reasonably fit me all things established.
The SystemSix although an old design now had proven to test well for many many years - it can also be found for pretty amazing price now.
At the end of the day I keep coming back to the Foil, It just looks so aesthetically pleasing to me, and has at this point in time up to date aero and is at a decent value and just plays the part.
The Winspace is a top runner, but it really isnt much savings at the moment over a name brand and does not have any testing data against it.
The SL8, well I feel that there is just so much hype and skewing on the bike vs a true aero bike and EVERYONE has a SL8 it seems haha.
Any reason why the Giant Propel or the Parlee RZ7 isn’t on anyone’s list? The Parlee is non-UCI compliant as it has shrouds over the disc brake calipers for aero but a review I read described it as an able climber, decently comfy and it looks a lot like a Venge so probably pretty fast. As for the Giant I’m just curious as they’re a big brand and usually well regarded but as far as how aero this aero bike is compared to the rest I have no clue.
BMC TeamMachine R begs to differ
Y1R? Do you have a link?
It may beg to differ but from a aero perspective that frame looks pretty aero compared to a Supersix Evo or SL8
The point is that an “in between” depth is as fast if not faster than a full aero bike with fat tubes.
Would you spec the Y1 R with 105 Di ? Nothing against that at all but I was looking at higher spec builds that would more closely line up with what a complete Y1 R might cost.
Good stuff for debates.
I can answer from my prospective, the Giant Propel was a prospective and is a fairly good value bike - it however just edges out of what I need from a fit perspective when comparing it to the others. It’s aesthetics also just dont do it for me.
The Parlee, it appears to actually be a great candidate and something I had not known about - they dont seem to publish pricing though.
Personally if I was going to drop money on a ~£5k frame like S Works, Colnago, Lab71 version of Cannondale, CFR version of Canyon, etc then I’d spec at least Ultegra and likely Dura Ace to go with it. I don’t think you’re getting much if any performance improvement with higher end groupset other than saving a few hundred grams, but then I would say exactly the same thing about a frame that uses high modulus carbon to save a few hundred grams over a cheaper version made in the exact same shape. Can’t possibly justify buying a Colnago in terms of performance for your buck, if you’re spending that money it’s because you want the best and that doesn’t mean putting 105 on it!
Seems a bit of a sacrilege to not spec this frame with the best and lightest components ones pocket allows
The top spec Foil RC Ultimate is $15K. Not the same parts but a top spec build that would be in the cost class of the Y1 R and the next build down with Dura Ace is $9K. You could definitely build a Y1 R with 105 but I do not think many people shopping a frame like that would do so.
