The 750 is a AFB that has a counter weighted air door. The problem is normally that the air door gets slammed open and there is not enough of a pump shot to cover it. You end up with a bog.
The 650 is an AVS that has a spring tension air door that can be tuned to open later or sooner depending on the engine needs. The problem, they only come in a 650, a good size for your combo, but small for future upgrades or an 800, which is too big.
IF this choice was put to me, it would be the 650 AVS and a K&N extreme lid that will help it flow more than the rating. A K&N stub stack maybe possible to use for more cfm.
You could rack up a few more cfm in this manor. Steve D. of Mopar Muscle did a test. I can not seem to find it now, but, the addition of the extreme lid and K&N stub Stack was a nice improvement. Here is some reading below.
