Just this last week I upgraded my son's computer from a 5770 to a HD 6850. Thanks to ebay, sold the 5770 for $94 Shipped and got the 6850 for $74 after rebate and selling free games that came with it (Dirt3/Shogun2/STALKER). So cost wise after eBay fees it ended up being about a wash. OC'd the 6850 to 960/1160 so it is about as fast as a 6870. Only done some limited testing so far, but performance increase is around 50% over the 5770 for most tests @ 1920x1200. As a matter of fact, according to this old review there are some games where a single 6850 is as fast as crossfired 5770's. I think that the 68xx cards have improved with drivers since this review as well.
So, some choices I would contemplate are:
a) Sell your 5770 for $70-80-ish and take your $130 and together get a GTX560TI or 1GB HD6950 or GTX470 if you can find one
b)Sell your 5770 for $70-80ish and use some of your $50 and pick a 6850. If that is not enough power grab a second for x-fire with your remaining $130 (This only really makes sense if you do not mind rebates and selling the included games).
c)Wait a bit longer for 7xxx, which may be another 4+ months out. Chances are the 7850 will be sub $200 which may outperform the 69xx cards....but this is just speculation.