I have i7 and 560 ti OC and I think it's slow in some games (crysis 2 with hi res textures and ultra everything) and I only have one monitor! So I don't believe a 590 is overkill, especially if you plan to play in higher resolutions or more than one monitor.
It would overkill my budget though... =D
I don't agree or disagree for that matter with earlier claims in this thread but I gotta tell you there is a difference between a 560ti to 590 and then as stated earlier 580 to 590, no offense. Either way we are not here to convince it to get a 580 instead but help deciding on a PSU.
i7-4770k - GTX 780 Ti - 16GB DDR3 Ripjaws - (2) HyperX 120s / Vertex 3 120
ASRock Extreme3 - Sennheiser Momentums - Xonar DG - EVGA Supernova 650G - Corsair H80i
build pics