I'm looking to build a new wheelset with some stiff modern Velocity Major Tom tubular's (decals removed) and VO high flange 126mm threaded hubs. They are 23mm wide outer so I don't want to run a 23mm tire. I may go with 25 but my frame/fork will clear a 28.

I'm not sure if 28's will clear my calipers. It's hard to measure but it looks like I have 7-8mm of clearance on both ends with my current 23's. Any way to estimate how much higher a 28 would be?