GTX250 or 260 ? Anyway with both you won't have DX11, so they're some sort of dead end.
I would pay 20 bucks above the budget and get a 6870.
Though if you're on a tight budget the 260 (x2) is a nice card for $60 and you'll even have a spare one then. You can't sli them with this psu and don't see your mobo, but a single 260 crushes a 6450. http://www.hwcompare.com/10312/geforce-gtx-260-vs-radeon-hd-6450-oem-1gb/