the highest you can go up to i have been informed is 264 degrees of rotation, before you have to machine the head, get new lifters and valve springs
tomei cams don't make a 264 they only make 260 and 270 or 272 (don't quote me on this though)
hks have 256, 264
whats been mentioned to me is that the 264 cams will be enough to get ya 500hp, anything more then 264 is really for darg machines with 700+ hp
adrian