I ran a 472/87 and a 476/92 on my truck, and I much preferred the 72 to the 76. I'm not sure how much was due to the compressor wheel change and how much was from the turbine wheel, but the 72 was much more responsive and made a little less power than the 76. If you have enough fuel, you can easily make 900 on a good 72mm turbo (that's what the time slip showed I was making); I was running 100% injectors and a 10mm cp3. If you want to add nitrous to it, you should be able to bump that up to 1000 hp without having to go crazy, and I think the 72 would be a lot more fun do drive as well.
I forgot to mention, this was all done on a very mildly built engine with a set of stock head castings and valves running SoCal valve springs and their standard fire 9100 cam (that is probably one of the best duramax camshafts available for a performance street application in my opinion).