I've tried both Japanese and US RX7 Corsair Vs and they're the same inside. Go to Cycle Gear in Fullerton, try a Corsair V, and if you like it, order the same size from Simon.I'm currently using Shark's RSR2 in an XL. The fit is ok, but not perfect. There are still a few slight pressure spots but nothing serious.
I've had the previous generation Arai RX7rr's, and the Arai Quantums, both in the XL. Although Arai advertises that the Quantum is for a more round head, I've had better luck with the RX7rr's.
I definitely would give the new RX7's a try if they made them fit a rounder head.