I've been experimenting with tire widths, from 25mm to 32mm. I've found that comfort and grip with 32mm is great, and doesn't give up as much speed as you might think. Obviously you need to have room to fit 32's, something to keep in mind, at least with the GP5000s I'm running is that they are not only wider, but also significantly taller than 28's.
I recently did two rides on our local 7 mile TT loop. Six laps, going hard, averaged 22.5mph on 32mm, and 22.8mph on 25mm, both GP5000s.
Same wheels/kit/position. On my wheels the 32's measure almost 34mm, and the 25's measure right at 27mm. Wheels are 50mm deep, 19 internal, 27.5 external. So not perfect 105% with the 25's, but close. 23mm might be a hair faster, not sure I want to buy another set of tires to test tho (if someone would like to donate a set, I'd be happy to try them out lol). Over a 43 mile, almost 2 hour ride, I saved about 1 minute with the 25's. Temp/wind/effort felt similar.
Not exactly scientific, but I don't think it's as big of a deal as people make it out to be, at least for average riders. Obviously, if you're chasing seconds and podiums, then optimize everything. I'll keep the 25's on the 50mm wheels for races and TTs, and keep the 32s on the stock wheels for training rides. If your roads are bad, like some are around here, I've found that you'll actually be able to go faster with the larger tires because they're more comfortable, and you're less fatigued from not getting beat up as much. The TT loop I used is pretty smooth, so that didnt' come into play.
Not trying to convince anyone, ride what you want and works for you, just adding some info for anyone who has been hesitant to try larger tires.
