I’m 150 and I have zero interest in riding 25’s anymore…28’s are just better. I’m also a pretty big aero geek and I’ll take the marginal aero hit for what a 28 gives me in ride quality any day.
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28 are more comfy
What are the OD of your aero wheels that you run 28’s on? Specialized put out an aero test video testing tire width and the aero loss wasn’t as much as folks make it out to be. Then you have the hard core 105% people.
Your posts are giving me hope for 28’s and aero. 
They are Reynolds Stryke wheels (came with the Canyon Aeroad)…IIRC they are 25mm external and 17mm internal. Tires measure at exactly 28mm on them (Conti 5000TL). I run them at ~70psi, but am starting to consider going down further.
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At pressures you can achieve with a tubeless setup the 28s are the way to go. But rationalization,appeal to authority, and cognitive dissonance rule the cycling world so let me give you some actual data to guide your decision. 
The weight difference between the 25s and the 28s is going to be on the order of 30 grams total. I consider that de minimus. On a climb you’re not going to know that difference exists. Especially considering the next point.
At tubeless pressures the 28s will have a couple watt advantage over the 25s in terms of rolling resistance. Maybe more than that if the road is a little rough. During a climb rolling resistance is relatively more important because you’re at a slower speed and aerodynamics matter less (as you know, just mentioning it for the sake of being complete).
And, finally, 28’s have the intangible advantage of added comfort. You should ride them back-to-back. 25’s first then 28’s. If the rides are proximal you’re going to notice that the 28’s MAKE A HA-YOOG difference.
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That specialized video seems to actually quantify the value of switching to an aero wheel given a fixed tire choice. The results being that aero wheels provide significant benefit regardless of tire choice.
I’d be interested in quantifying the cost of violating the 105% rule. Given the wheels I have, what’s the difference between 25 (which are nicely under 105% the 27mm outside width), and 28 or even 32? I have yet to be able to find a real answer to this, but I’ve definitely read dire warnings along the lines of “all aero benefit is nullified of you go too big.”
Exactly. So I understand the video the same as you. I don’t mean to throw this thread off topic, but I brought up idea of running aero wheels for gravel. Got many passionate replies that it’s a waste because of the 105 rule. But specialize’s test negates that. Maybe the 105 rule was for TT setups where you are ringing out every last benefit? 
If that’s the case I want to finally just ignore the 105 rule. (I dont TT)
My understanding of the 105 rule was that 105% was for maximum aero benefit, and not that there was no aero benefit if it was violated.
Hell, plenty of guys have been violating the 105 Rule in Roubaix for years…
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I’d also like to ignore the rule…but I’ve found it’s very difficult for me without some data (totally irrational, I know).
I’d love to find something that says gains from adhering to the 1.05 rule are roughly equal to ceramic jockey wheels.
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Well, that’s it. I’m ignoring it now . Now if it’s easy to accomplish then fine. But I’m now happy to ignore it to run the 28’s. Thanks folks! 
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I’m running Specialized S-Works Turbo Rapidair 2Bliss in 28 on a set of Enve Foundation 65’s (external width of 28mm). Enve recommends 25s for maximum aero benefit, but there is some difference from tire to tire in terms of actual width. The S-Works in 28 that I’m running measured 29mm on the calipers when installed on the Foundation 65’s, so very close to matching the outer rim diameter. On Saturday I rode them at 56 psi and they felt fantastic (rider weight about 155lb).
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I just went to 28mm GP5000 TLs from 25mm Schwalbe Pro One and I think I’m a fan. The 28s feel just as fast to me and are definitely more comfortable.
My 25s ride nicely at 70 so I’d definitely think you could go lower.
Still, nobody seems to have real data on rim matching to say just what you are giving up putting 28s on 25 mm rims.
Surely someone has done some quantified on road TT testing with GP5000s, but if not, maybe I will try it at some point, comparing 25 vs 28 on 28mm OD rim. (On which 25s are closer to 26.5, right on the 105% rule).
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Finally a response mentioning rider’s weight.
I’m 60kg and running a wheelset with 27mm outer diameter. After a lot of googling I have concluded there’s no clear benefit to go wider at a particular weight and a tested constant comfort level. I think it was from BRR website.
I guess in short a 25 has better marginal aero benefit than 28 with the same comfort level, at least for my weight and rim width, theoretically speaking.
I’d probably try out a 28 when I’m ready to splurge on a new TLR wheelset with wider outer diameter that’s optimised for 28.
Forgot to mention my current 25 running at 72 psi rear and 68 psi front.
That is what I’ll be doing with my new wheels. I’m a lighter rider as well (66KG)
So you’ll continue running a 25?
I am on 28/28 with my current 32 mm depth wheels. My new wheels will be 46mm depth, so I’ll switch to 25/28.