ATI HD5870 CPU Bottleneck

Hi everyone,
Hers my long story xD,

I am willing to buy an HD 5870 because I sold the GTX280. Also, I am getting the HD5870 because of the support of 7.1 DTS/DD sound over HDMI 1.3 as opposed to the 2.0 on the GTX280. The GTX280 was smelling plastic on full load in crysis and at Folding@Home lmao. The cpu is the Q9550 E0 stepping but...with an HP worksation xw4600 that I got an amazing deal on.So the 4GB-800 is ECC for servers. There is no way to overclock in the bios. The good news is that I found a way to overclock by software( No! clockgen dsnt work) by looking at some chip on the motherboard using setfsb but that will simply raise the fsb and overclock CPU,RAM,FSB @ the same time. Luckily, I got the Q9550@3.5Ghz@1.2V and the ram @1Ghz stable @stock voltage for sure. There is no way to change the voltages and I do not justify the money on buying a new motherboard with new ram. PSU is a Corsair TX850 and 3x500Gb RAID0. Chipset is X38 Express. Monitors resolution is 21.5@1080p. So, will the Q9550@3.5Ghz bottleneck a single HD5870?
And is there a way to flash the motherboards bios or tweak the voltages by software or hardware?
Last question, does the HD5870 speedup video conversions like the GTXs?(MP4->AVI->DivX->Mpeg4->MKV...)

Thanks for your time.   and no I did not join the forum on Tue Jan 01, 1970 LoL