I've tested XP Pro, Vista Home Premium and Windows 7 Ultimate (all 32 bit) on same specced virtual machines. While XP performed best (boot time, file copying and opening applications), Windows 7 was a close second, with Vista lagging waaaay behind.
As far as your laptop goes, installing XP could be problematic as far as drivers go. I've had huge problems getting XP compatible drivers for audio and video chipsets for laptops which were built for Vista. I've experienced no such problems upgrading to Windows 7.
If you want to retain all the manufacturers features and bells and whistles of your laptop and you have the recovery disk, I'd recommend recovering Vista and then upgrading to Windows 7. It's a very clean upgrade... takes about 30 minutes. Run Windows Update two or three times where as well as security updates, it also picks up upgraded drivers for touch-pad, audio, video etc. All in all a painless process. I've done this on seven or eight machines over the last couple of months (Toshiba, Acer, HP) without a hitch.
As far as Windows 7 'try before you buy', I must admit to testing using an 'acquired' copy
The copy I used was well scanned for malware, rootkits etc. and came up clean. It even activates successfully
PM me if you want a link to a safe copy (don't want to breach forum rules by posting here).
Growing old is mandatory... Growing up is optional.