I'm pretty sure it's still at stock speed as I was having trouble getting it past 4ghz and reset everything to default. I take it if I could get a decent oc on cpu may raise score slightly. Also my score was marginally higher than most other xfire scores and I was in x16/x4. Would x8/x8 make a big difference to the performance. Most reviews I find claim there would only be a minor dif to the tune of 3-5 fps
Ocing the CPU often makes a big difference (otherwise your GPUs will be bottlenecked).
As to x16/x4 or x8/x8 you need to post more info - what mobo, cpu and if you are using PCI-e 2 or 3