^ second that, 850 for 1 4850 is far more than you would ever need, the recent 1kw psu review done by xbit proved that the general 'forums' opinion on what wattage psu you need is quite a bit higher than necessary, i.e. 750w would be more than enough for x2 of your cards or x2 4870s or 260s. In terms of PSU i have always had TT tough power psus and none have failed me yet, I even ran 2 1gb 4870s on a 600w (might of been 650 cant remember) one and whilst the 12v rail was very low it still didnt fail me under heavy load. Now have swapped to an corsair hx 1000 which is mint, so either of those brands I would reccomend. If you want to save money than TT is a fair bit cheaper than corsair.
EDIT: I would also get a modular PSU too as so much better case air flow and tidyness without having 1/2 a doz molex cables your never gona use floating round. well no, I never use them some people do for fans and old hdd and optical drives.