if it an everyday car I would stick with the vacuum secondary...
my experience with vacuum secondary vs double pumper is the dp is about .10 faster...
but my converter flashes to 5000 rpm and 4.86 gears...
check out the Quick Fuel Technology adjustable vacuum canister for the 750 holley.
http://www.quickfueltechnology.com/main-body-parts/quick-set-adj-sec-housing.html
can adjust opening using the needle and seat screw....can be easliy change between strip seting and street setting...
another thing to do...is see if you can borrow an 750 double pumper ???
