I suggest 215/35-18 in front. You're unlikely to rub with 215/35-18 in the front; most folks don't. When you go to 225/35-18, that significantly ups the chances of rubbing.
I would also suggest 265/30-19 or, at most, 275/30-19 in the rear. The NSX handling seems to degrade when the stagger (difference in treadwidth, front vs rear) is 50 mm and even more so above that point.
Remember, the biggest factor in tire performance is the make/model of the tire, not the treadwidth; a stickier, narrower tire almost always grips better than a less sticky, wider tire. So for performance purposes, concentrate on buying better, stickier tires, more so than wider tires.
The best street tires available in 215/35-18 and 265/30-19 (and 275/30-19) is the Pirelli PZero Nero. The Tire Rack has them on closeout right now, so get them while you can; fronts are only $80!