3 way GTX570 With NZXT Hale90 1000W?

Plug your specs into one of these:

http://www.antec.outervision.com/
http://extreme.outervision.com/psucalculatorlite.jsp

Both only allow me to enter SLI (not 3 way SLI) and they both came back with a recommended PSU wattage of 835W, say a third GTX570 adds 200W under normal gaming conditions then I'd be over by roughly 35W (1035 Total).

How accurate are these PSU calcs?

Those calculators always overcompensate. If the GTX570 consumes 200 watts under typical gaming load then 3 of them (in theory) would consume 600 watts which should leave 400 watts for the rest of the system which again, should be more than enough power for your i7 and stuff.

I need a Watt meter I think.