Go the HP.
Other features are:
4 corner idle
Non stick (re-useable) gaskits (blue), and nylon bowl screw gaskits/washers
Notched floats and fuel extensions (good for hard launching)
Power valve blow out protection
Special dichromate & polish finish for smoother flow
They are US$629 new. I got mice off ebay motors as new - only had a few dyno runs on it for US$425. You're probably looking at AU$600'ish landed in Oz. Or you can get ripped and pay $1300+ here.............geee, let me think?
example (there's always heaps there):
For info, the 750DP part # is: 80528-1. The last digit "1" varies from 1 to 3. It designates 1st, 2nd, 3rd edition, with slight improvements on each. Mine says "2", but not sure of specific differences. Email the Holley hotline for info.