I have a 440 Challenger.

I bought my challenger from a guy that slapped a 600 cfm on there. I need a 750cfm, im between a rebuilt holley 750 or a Holly double pump 750 is the double pump worth the extra money.

P.S. I have a single plane intake with small cam and Exhaust work.  

Really for a 'built' 440 I would use around 830-850cfm.
But for hot roddin & cruising around town [or not going for max power] a 750 dbl pumper is what I recommend.
Cause a properly tuned dbl pumper will always out perform a vac secondary in wide open/off the line acceleration, which is why [if rules allow] the the dbl pumper design is the choice of racers in the winning circle.
And hey how about that 4 corner idle? gotta love that [unlike 2 corner vac secondary].  

750 double pumper is definitly worth the extra money over a vaccum operated carb, especially on a big block.