I believe if you search through the HiPo section you will find that most racing applications use the 18,18 combo, but then you need to modify the triple or fork length to get the geometry correct. If you want a bike that handle like stock then go stock sizes.
Yep, here's a pic of my gold K2 which was built by Ken Piper, an old race bike builder and mechanical engineering lecturer at the Australian Defence Force Academy. It's fitted with 18 inch wheels front and rear, and was (I sold it a couple of years ago) the best handling CB750 I've ever ridden. (and I've ridden a lot)
Back in the day, the accepted wisdom was that same size rims were the best option for racing, but that might have just been to "quicken" the steering, I really don't remember.
There are lots of really good 17 inch wheels out there, and because of their availability they're really cheap too, but there's a problem with using them. Our engines are really wide compared to modern engines (BMW's new 6 cylinder engine is narrower than a CB750 engine) and by lowering our bikes with 17 inch wheels (and modern forks) it reduces the ground clearance and lean angles significantly.
That's handy if you're building a minimalist custom "bar crawler", as you won't need a sidestand, you can just lean it on your alternator cover, but not so good if you wanna go around corners. Cheers, Terry.
