It's the same installer, so the difference must be in the install or hardware, as suggested.
I wouldn't settle for less than instantaneous performance with Windows 7 because that is what we've become accustomed to in over a year's testing experience.
Troubleshoot your Event Viewer errors, study the Diagnostics Performance log (by clicking WEI score at Computer>Properties, then choosing Advanced options) and Generate a System Health Report.
Check for newer drivers
in optional Windows Updates, on your computer or hardware maker's website.
Run the Diag/Repair CD for your HD, full scan: http://www.tacktech.com/display.cfm?ttid=287
Run memtest86 overnight to stress test memory.
Run sfc /scannow to check integrity of System files.
Run a Repair Install
as a last resort before clean installing with HD deep clean.