Not a good value ATM. If you can get a 5770 for only $10 more, why wouldn't you? About the only reason I can think of is if you were building a "green" PC and wanted the fastest card available that didn't use an external power connector. You'd be cheating yourself out of a lot performance for the sake of $10 and a slightly lower power bill, though.
As "value" that's correct if "building" your own rig; although wanting a simple upgrade for an OEM box it's "value" shines. No PSU and in most 'cases' not needing to add an extra fan. If you go 5770 you'll need added air flow in an OEM enclosure, even if you get a rear exhaust cooler I'd still say you'd want more air.
If the idea is building a "Green Gaming Machine"... I actually would consider that an oxymoron, because if your aspiration is to play games... then build it to play games! Embrace the idea that power/FpS = fun! To purchase an item(s) that aren't fuelling the true visceral craving, will have you walking away not feeling the vigor to play.
That’s opposite of "Green" as the energy to produce-deliver the component(s) in that machine is wasted (more or less). Such parts in all probability will get removed before their time, renounced, and finally disposed of, never fulfilling their true design… and most likely in a land-fill. How is that Green?
Green is to understand the need and accepting only after properly consideration of parameters of a required design. It’s like buying the wrong truck when the intention is tow a big-azz trailer. You'll end up using more fuel/parts while doing so. Burning out that truck early just means it will see the crusher that much quicker, there’s nothing green about it.
Green is overused... smarts' not so much.
Sincerely,
CC