ussually my formula for a good cruise with a little get go is the closest size down from dennys power method... say a 351x2 is 702 so i'd run a 650... thats ussually a good way to get something that'll cruise well tune in easily but still pick-up when you want it to.... if you went with a 700 on that formula, it'd be a lil more work to dial it in, but it'd run at top RPMs a lot better