I doubt you'll have to have dual pumps for that I run dual D5's just because I can lol I have a dual alphacool D5 rez. Running dual loops.
I see more 45's than I do 90's in your rendition. 45 from lower rad to gpu2 45 from gpu1 to sb (total waste imho) 45 from vreg (another toal waste imho) to upper rad. and 45 back to rez the only 90's I can envision would be sb to cpu and cpu to vreg and most likely pump to lower rad. I see at least 3 90's rest being 45's or straight.
The 90's will knock some flow rate down but not enough to have to worry about it.