Im looking to upgrade my system and Im not sure whether or not I need to buy a new power supply. Right now I have a tx650. The new system would be a i7-2600k in a gigabyte z68 ud5, 8gb corsair dominator and a 580gtx. It would also be running about 8 120mm fans (corsair h100 push pull). Id also like to have enough room to overclock. Most of the power supply calculators out there tell me Ill need about 900w. That just seems high to me. Any thoughts?