In response to your question. I can only give tell you from experience!
I replaced my old graphic card to a MIS GT610 on my HP a6177C. It has a ASUS motherboard mini-atx IPIBL-LA. I have done some upgrades over years, including upgrading to a 600W power supply (HP power supply fan made too much noise), Replaced the Duo Core processor with a QuadCore Q6660 and added 4GB of ram . I am running the system in 32 bit. Yes, It is not a gamer rig but GT610 handles very nicely. It is hook up to a Dell u2713hm monitor and it handles 2560x1440 beautifully in windows 8, Vista (I use it once in a while) and of course Xubuntu (Which what I used the most) . I would think you wont have any problems with the lower 600 series Nvidia. The GT610 is both low in power consumption and low profile. I had a GT520 before but the fan noise was horrible but it never failed me.
Good Luck! Hope it helps!
MIS GT610 is about $50.00 1GB
Using Xubuntu 12.10 (Nvidia driver 313.30)
Nvidia X-server sees it as:
PCIe x 16 1st generation Max 2.5GT/s
Sorry I did not read the full threat. I have no games in the system. It plays Blu Ray and media beautiful. Games not sure it is ddr3 so i am guessing probably not!