Some things :Graphics: Card: Advanced Micro Devices [AMD/ATI] RS780 [Radeon HD 3200] bus-ID: 01:05.0
X.Org: 1.15.1 drivers: ati,radeon (unloaded: fbdev,vesa) Resolution: firstname.lastname@example.org
GLX Renderer: Gallium 0.4 on AMD RS780 GLX Version: 3.0 Mesa 10.1.0 Direct Rendering: Yes
- the driver ati listed suggests you may have remnants of the amd proprietary driver that slow down things
- mesa 10.1.0 is the first of the 10.1.x releases, there have been 6 bugfix releases after that one.
You could ask help on Mint forums to check out the first issue, and also how to upgrade to mesa 10.1.6 .
About a new card :
if you go nvidia , use the proprietary drivers. nouveau (nividia opensource driver) still lacks many features / performance.
Your processor seems a bit old (2008/2009 ? ), if you go for a recent videocard it's likely the processor will become the main bottleneck, preventing you from using the new videocard effectively.
Unless you intend to put the videocard in a new system in the near future, I'm inclined to suggest you look for a card that's a few years old.
for amd cards a card in the HD6xxx / HD7xxxx (Southern Islands chipset) range should bring lots of improvement without the cpu becoming a big bottleneck.
sorry, can't help with nividia card types.