Which should I get - 4870 vs 5770

For the past 3 years, I've been running fine with my 2.8 GHz E6550 coupled with an ATI HD 3850 256 MB. It's been enough to play all games at my monitor's native resolution of 1440 x 900, with some games in lowered settings (Crysis, NFS Shift, DiRT 2) and is able to run most not-so-demanding games at max (TDU, COD Series, AC2). I thought it'd be enough until I replace my whole rig in about 2-3 years.

However, this summer my LCD monitor broke and I had to buy a new one. As LED-backlit LCDs are now reasonably priced, I got myself an AOC e2236VW which has a native resolution of 1920x1080. Now, my card has a hard time running things at native resolution, though I can still run older games like TDU and COD4, as well as newer non-demanding titles like CODMW2 with 4xAA and 16xAF, most other games have to be run with no AA anymore. Actually, the even more demanding games (e.g. NFS Shift) have to be run at 1280 x 720.

In other words, the 3850 256MB was and is a great card for resolutions no higher than 1440 x 900. However, I think I have to make a mid-life upgrade of my rig. The choices are down to 5770 and 4870, both 1 GB versions. I don't think I should go any higher as I'll be CPU bound (my board is just a P5QL-Pro and isn't very overclockable, so 2.8 GHz is the highest stable I can go), and more importantly, financially-bound.

From what I see, the 4870 is still faster than the 5770. They say the performance differences are negligible, but 4-8 fps per game is actually significant especially once they start getting old as I'll be needing to squeeze as much performance as I can from them. Of course, most people will say that I don't buy previous-gen technology, especially as the 5770 has more features. However, I don't need any of these features. I don't bit stream my audio, I have no need for Eyefinity, and DX11 isn't much of an improvement over DX10 yet. The only significant benefit of the 5770 is that it uses much, much less power.

So right now, the issue is: significantly more powerful old card vs greatly more economical new card. Given this, I'd probably pass up the few FPS for energy savings. However, there's another issue - PRICE.

Brand new 4870s are hard to find nowadays here in the Philippines, so I'll most likely have to settle for a 2nd hand unit. A 1GB 4870 costs somewhere between $100-120, with rare $90 ones coming up once in a while. I'm not really familiar with the difference between reference boards and those with custom set-ups, so I don't know if the cooling differs much. Is it a big difference? Anyway, the 5770 on the other hand, retails for around $160 brand new, and the 2nd hand price range is around $120-$150.
From my perspective, that's a very significant price difference. I also think it offsets the extra power cost of having a 4870.

So, this is my dilemma, and I would really appreciate feedback on which I should get - a 2nd hand 1 GB 4870, a brand new 5770 1 GB, or a 2nd hand 5770 1 GB. Thanks.