Dell Studio 1557
Processor: Intel Core i7 720QM 1.6 GHz
Mainboard: Intel PM55
Memory: 4096 MB, DDR3-1333
WDC WD3200BEKT-75F3T, 500GB 7200rpm
Windows 7 Professional 64 bit
Cubase 5.5.1 in 32 Bit.
I find that it can handle about the same amount of plug-ins (even if I just use Cubase plugs) and audio tracks as my 4 year old white Bootcamped XP Macbook 13" with a Core 2 Duo 2 GHz processor, 5400rpm drive and 2GB RAM.
You didn’t mention perhaps the most important thing: what soundcard do you use? What soundcard driver do you use? Have you tried to adjust the audio buffer setting? Anyway, you can check some general DAW optimization tips for Windows (for instance) here: http://www.focusrite.com/answerbase/en/article.php?id=1071
Changing buffer should help a little.
It’s not a system I have, but you could turn off any power saving options in the Bios and make sure hyperthreading is enabled as that is what is supposed to give performance advantage over older quad cores and having read the review watch the temperature when under load.