I'm a complete PC novice so sorry if this sounds dumb.
My desk top PC has a ATI HD3870X2 fitted. I want to swap this for a DirectX11 compatable card. Would the ATI HD5670 be a good straight swap (connectors, etc.) or should I look at a different model?
What is your budget and the overall specs for your current system? With this info, we can make better recommendations. Kari is right regarding the performance of the 5670, there are better (stronger) inexpensive options.