800whp can go with pretty much any set of commonly known pistons and rods. Given an 800whp goal I'd go with Eagle rods and a set of Manley, CP, or J&E pistons of the appropriate bore size for your block and dish to get the static compression you want. Generally speaking it's safer to go 0.5mm overbore right from the start and go with 86.5mm pistons right out the gate vs trying stock size pistons and hoping the bore is clean enough to need no additional machine work.
While building it, I'd strongly advocate that you include a PHR or similar upgraded oil pump, a billet timing belt tensioner bracket, and an ATi/Titan or Fluidampr crank pulley. Combined with stock sized ARP studs, main studs, and a Toyota genuine 2JZ-GTE factory head gasket you'll be good to 1000whp/800wtq without any fuss and for a good long time.
Depending on your turbo setup and intended fuel, you can still crack the factory mains at 800-850wtq, particularly with E85 and smaller turbos that spool stupid fast. For 800whp you'll typically see 600-700wtq on most turbo setups so that would not be a risk for your stated goals.
Billet mains do add some cost, but are excellent future-proofing and 'peace of mind' for any potential project creep or future goals you may have.
I agree when doing a rebuild its better to just go 1 size up on the piston bore and have the block bored/honed to accept. You will start off with a perfect cylinder surface like a new engine. Because the engine block is already being machined, you might as well go with billet mains. That adds some extra machining to the block but well worth it to just be done with it.
If you're willing to go this route, you might want to look at built short blocks for sale from the different reputable engine builders people recommend on here. You exchange your stock short block for their built short block. Saves you the hassle of trying to figure everything out. Many different packages out there for different power levels.