on that board as long as its in one of the blue slots you're fine
There's only one blue PCIE x16 slot. The second slot is x4 but it is a PCIE 2.0 motherboard. There will be a performance difference but it will be small. Here is an article on the subject where they tested an HD5870;http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/25.html
A slot like the one your card in limited performance by approximately 5%. The HD5870 needs slightly more bandwidth so it may be a lil lower for your card, unless you have it overclocked and then it could be a slightly larger hit.