Oops I made a mistake my psu is 300w not 350w though the ampere ratings are same(+12v 13A,+12v 9A). I'm currently having 8600GT ddr3 with max power 43W. 5670 will add +20W. Will it be inefficient? http://www.extreme.outervision.com/PSUEngine
calculates recommended power as 226W so I should be OK I guess.