(2)450 DP's vs (2)750 DP's

I agree with what newbomb Turk said also about installing annular boosters on your 750s, I would go with 16 hole. I use 12 hole on my 470 with 2-850s and my fuel consumption numbers on the dyno are outstanding.
You can even jet down smaller with the annular boosters too which might even pick up mpg with your 750s.