You can't use the Dell bios, it's different...
AW somehow limits the clocks on the video cards for the m9700 through the bios, but there are people with Evesham systems with standard oem bios that allow coolbits to be used, and they've posted links to the bios' here before.
I'm not sure how AW limits the clocks, but there is always a way around it if you don't mind voiding your warranty.
I read one review recently that said overclocking a single card in the m9700 yielded similar results to the SLI on standard clocks. The implication the author made was that the SLI was limited by the single core turion processor. I'm not sure I agree with his conclusion...
I haven't seen anyone that has overclocked an m9700 get close to the clocks the Dell guys are claiming with their setups. I think the cooling solution may be more robust with the Dell allowing more room for safe overclocking.
My system is in shipping now, as soon as I get it I'll be playing around with it quite a bit for benchmarks. I'm hoping to compare single card benchmarks with OC single card benchmarks, SLI at stock settings, and SLI overclocked.
The only guy I know with the 512 cards though is aaronjb, and he wasn't able to overclock his system much... From what I've seen mid 400's/1200 range is more like it for this setup.
Read his review and posts in the review section, also marker01 did a bit of tweaking I think.