Unless you are going for all out power, the factory style compounds outweigh a single in many many ways.
Agreed with Ron. There are people successfully running a single in many ways on 6.4's but the VGT compound setup is really hard to dislike IMO. I'v watched workstock 59/76 elite compounds with a dual fueler kit and 60% injectors make over 800 on fuel and go 11 seconds all day long and the drivability they have is unmatched compared to say a single s468 or s472 with the same fuel setup. The compounds will light faster, be better on the street and be more fun all the way around in general. That being said, Mike Corsilli from MPD has done some really crazy stuff with his single s476 6.4 truck and Taylor Overcash has one of the fastest 6.4 race trucks ever using a single s476 and now a single s480. Pulling trucks also tend to use single turbos but I believe that to be for lots of top end power.
I honestly believe if you added a 59mm VGT HP turbo from elite to make your setup the Jr. High Powers and add a dual fueler, you would make around 750-ish HP and it would be everything you want it to be. Hopefully your motor and trans have been modified to live with that amount of HP.