Carb selection depends on tons of variables and one of the biggest IMO is intended use. In my case, a 340 street/strip combo I have tested at the strip with a 650dp and 750dp mighty demon. Both carbs were set up to drive on the street at 13.5 to 14:1. WOT was setup for 12.4 AFR. I run an rpm airgap (dual plane intake). To get the AFR as equel as I could in all 8 cylinders I did a lot of testing reading plugs at light cruise and WOT. The different runner lengths to each cylinder required stagger jetting to get each cylinder as even as I could. I say as even as I could, because the AFR meter just aft of the header collector is an average of one bank and two cylinders are feed by the deep side, and the other two by the shallow side of the intake manifold. I ended up running 4 different size jets in each hole. Long story short the 650 always has a better 60' time over the 750. The 750 always produces a 1 1.5 MPH increase at the 1/4 stripe. For my combo the 650 is best because the ET and consistency is better, (my intended use).
Seat of the pants feel in my case did not work in my car. One day I made a change on the 750 and went for a ride and thought I finally found the magic tune. It felt better than the 650 driving around town. Went to the track and the 60' and 330' times were slower than the 650'. I don't know how much time I've spent changing carb and timing settings trying different setups but it doesn't matter to me. It's a hobby for me to always try and tweek a little more power from my combo.
If I were you I would stick with one carb for testing and get the optimum tune on the engine without your device installed (baseline). Document all jetting, air bleed sizes, pump cams, nozzle sizes, etc.
Install your device and tune the motor again. I say tune again because if you atomize the fuel better then less fuel will be required to make the same power. Document all the settings again.
Go to a dyno and run back to back tests on the same day and you will have better data than now.
