I would like to replace the graphics card in my 6-year old PC, however a lot of the interface standards and component technologies have changed it this time.

While I am fairly sure about backwards-compatibilty, I have no idea how a new card's performance might be reduced due to such discrepancies. For example, my motherboard has a PCIe 1.0 x16 slot, but if a newer graphics card has a PCIe 2.0 interface then how much will its peformance be compromised? Even though the specs look much better, could such a newer card be rendered less-capable than the existing card?

I have a fault with my PC and the exisiting graphics card is the likely cause but I am not 100% certain that a new graphics card will solve the issue. I am also on quite a tight budget. (I would like to spend around GBP 30, but could be stretched a bit higher if the extra was worthwhile). So I do not want to spend more money than I need to on a card that will be over-specced in my system and for my needs. But likewise, I do want a card that will be a considerable improvement on the current one, and will comfortably perform the tasks I require of it.

My PC specs are currently: Mobo: ASUS A8N SLi Deluxe (with 2 x PCI-Express x16 slots) - PSU: 550W - CPU: AMD Athlon 64 X2 4400+ 2.2GHz dual-core (1MB L2 cache) - RAM: 2 x 1GB DDR 400MHz (PC3200) (although I am considering later upgrading to 4 x 1GB) - OS: Windows XP Professional (32-bit) - Monitor: HD, 1920 x 1080 resolution, 24" diagonal, with DVI and HDMI inputs.

Current graphics card: nVidia GeForce 6800 GT (350MHz clock, 256MB DDR @ 500MHz, 16 pixel pipelines)

My needs: Photo-editing (a lot!), some video-editing, casual playing of older games.

How much will my motherboard's PCIe slot affect a PCIe 2.0 card? My system uses DDR RAM, does it matter if the graphics card has GDDR2 / DDR3? Will I see any benefit from a graphics card with 1GB memory, instead of 512MB? I have seen people suggest that on budget cards the extra half-a-gigabyte would be redundant and thus a waste of money. Can I use a card with a 64-bit memory bus with my 32-bit OS?

Thank you in advance for any assistance.