That would be fine. I have used and liked all the Antec PSUs I've had. But remember, with that unit you will be limited to 2 cards that only require a single 8/6 pin PCIe pwr cable each (like your 2 x HD 7770s) or a single card that takes 2 8/6 pin cables. Not an issue probably, just thought I'd mention it. Oh, and remember that it doesn't come with a power cable. They assume you will be using your old cable. http://www.antec.com/pdf/flyers/EA650_Green_EN.pdf
What do you think about this one: Corsair TX650W V2? I can't find what type of connectors it has and if it could support crossfire of 2 7770s.It seems to be quite a deal.
Corsair TX650 V2 has been discontinued, which is perhaps why there are deals to be had. It comes with 2 (6+2) PCIe connectors which is perfectly sufficient for 7770 Xfire. It's a good unit, if it's on offer for a good price then definitely grab one.