My current config is:
Abit KN9 Ultra+Athlon 64x2 4200+ (2.2 GHz) 1MB Cache
2x1GB DDR2-666 which I plan to replace by 2x2Gb DDR2-800
Nvidia 7600 GT, 256Mb (which I use mainly with the proprietary driver, I find the performance of nouveau not too bad, however it is not stable enough).
I plan to change my graphics card and to use the free driver. I am looking at an HD6770, 1Gb. The performance on R600 as seen on phoronix benchmarks seems very good to me. However these benchmarks are run with much more recent CPUs so I am not sure what to expect for the performance on my system. I don't plan to run commercial games but I would still like to be able to play something of the level of 0AD or Lugaru HD. Do you think I will get a decent performance or that my CPU will not allow my HD6770/R600 to get much more performance than on 7600GT/Nouveau?
Also I am interested on how good is the multi-screen support? I have seen HD6770 cards with 3 ports (HDMI+DVI+VGA). Can I use any combination of 2 ports out of the 3 for a dual screen configuration with R600?
Overall should I expect a good stability with the free driver?
Stability is great, and if you don't mind scaling back a bit when it comes to effects and resolution, pretty much everything is playable. (I played through Crysis with an Evergreen and r600g about a month ago).
I've switched from a 7600GT to my HD 5770 with OSS drivers a few years ago.
2D performance went up, it's very stable, and by now there are lot of 3d games that run well enough (native or wine).
On the other hand, you're switching drivers, so there's bound to be a regression somewhere. Don't expect miracles.
Going from my Athlon 64 X2 5000+ to the FX 6100 didn't have much impact on gfx performance. I don't think the OSS drivers use more CPU power than nvidia's drivers do. I think you're safe.
Haven't tried 0AD or Lugaru HD, so I can't comment on those specifically.
Multiscreen-support works flawlessly with 2 displays, much less hassle than I remember having with nvidia. Proper xrandr-support ftw! I think any connector combination works (at least the GPU supports that), but there may be cards out there where the connectors are wired in a weird way. Check the manual before purchasing.
If you wish to use three monitors, there are restrictions which ports you can utilize - usually, one of the monitors has to use DisplayPort, since the GPU can only output two non-DP-signals at a time. There are some cards with a builtin signal converter that bypass that restriction though.
One screen HAS to be DisplayPort (for 3 screen Eyefinity), and a cheap way around this is a DP > VGA adapter, they HAVE to be active as its impossible for it to be otherwise (Active DVI/HDMI cost around $100!) and most Flat pannels have VGA in
My plan is to do the following
DVI > VGA
HDMI > TV
(Thats my two "Legacy Screens")
DP > VGA > Third Screen
I've seen videos in Youtube proving this is possible