years ago i changed my forks to CB900 lowers so i could use a real caliper ( ended up with the rear caliper off a CX650 , which was a 2 piston sliding style, the spoked wheel precludes the use of an opposed piston style ), it bolted up straight to the fork leg but was slightly lower so i had to have the disc radius reduced by about 8 or 10mm. while that was getting done i had the face grooved with 4 grooves per side.
it wasn't exactly what i wanted but still worked immeasurably better than the stock setup and was way better in the wet due to the grooves
on my current build i have again used CB900 lowers with a single disc but i used a VFR800 wavy disc and a Braking brand 4 piston caliper which fitted with a small bracket to push the lower mount point out about 40mm. the disc is about 300mm which probably isn't that much bigger than a stock 750 one but its thinner, lighter, grooved and drilled. i expect much improved performance. i'm using an XR600 master cylinder, not sure if it will be big enough to give the solid ( some say wooden ) feel that i prefer but thats an easy change later if needed
