for best "flushness" you want 17*7.5
+15 or so. You can get away with +20 or +22 (on 7.5" wide) and looking flush, but you won't get that JDM tyte style unless you go +15 or +10.
I'm running 15*7 +5 and that's just about perfect! Effective offset in front is -1 (using 6mm spacers to clear brakes) and in the rear I have 16*8 +36 with a 3mm spacer (can't get f-ing studs off to replace with extended studs!) and it's not nearly flush. I'd say I need 15mm more neg. offset in the rear, making it about +20 or thereabouts... on an 8" wide wheel, that is. so 7.5... yeah, +20 or +15.