you cant have both worlds. a 350 with a 750 will pull in the high rpm range. i cant imagine how going to a 600 would kill throttle response. i run 600's with 62 primaries . you'll get quicker throttle response with a lean tune. even using edelbrocks formula a 350 only needs 600 cfm a 6k rpm. tune the 600, you'll get better millage and a cleaner burn for street use. that 750 will wash down your cyclinders and cause ring failure.