Latitude E6500 virtualization performance + new heat issue with BIOS A18

I have an E6500 with 8GB of memory and running Vista x64 SP2. I am able to enable the "hardware assisted virtualization". All virtualization options have been enabled in the BIOS.

My main problem is that the performance in the virtual computers fluctuate a lot - task manager in the virtual PC fluctuates from 0-60%, all of the time. The Windows Task manager works (in any version of Windows) by showing how many simple cycles it can do in a second, idle priority.  The physical host fluctuates from 0-5%..as any normal PC. If I play any sound/MP3 in the virtual PC, I get a lot of snaps in the audio. Even just starting an old virtual Windows 2000, one can see the "progress bar" change in speed all the time.

My E6500 came with Windows 7 professional, but I experienced the same problem there - so I went for a downgrade, which also enabled me to run Virtual PC 2007 SP1 (with the hotfix rollup package also installed) rather than Windows virtual PC. Unfortunately, downgrading didn't help. Also, upgrading from BIOS A16 to A18 didn't do any difference either. I'm running with a P8700 CPU, and hardware assisted virtualization is enabled in the BIOS. In fact, since I've changed from A16 to A18, my E6500 has become warmer and the fan hasn't run since. I was so enjoying having the coldest laptop ever...

My normal (non-Dell) desktop PC, running Vista SP2 x86, doesn't behave like this - same virtual computers behave as fully normal computers, no fluctuation in virtual performance in any way. My normal PC has a Duo core 2 E6700 CPU, running with 4GM of PC800 memory. The services "Windows Search" + readyboost + superfetch have been disabled on both computers to allow Virtual PC to have loads of memory available + 0 waiting time on the hard drives.

So why is the performance so bad with the E6500? And why not let people decide if they want a cool PC, or a silent PC - with a user setting in the BIOS?