I spoke to Ray Barton about this subject when I was choosing parts for my 540. He suggested 10.5 with the 250* cam. I thought I wanted more comp than that, but he said the extra hassle with the fuel wasn't worth the few extra ponies.

I took his advice and my mild street 540 made 700hp on the engine dyno. I run 91 pump with no problems. I probably could have went with more comp and still used pump premium, but you never quite know where the line is between just enough and too much.

Anybody have a program that can figure the difference in HP between 10.5 and 12.5 comp ratios on the OP's combo?