Cores vs GHz

Hello,
 
After using Sonar on my Dell Inspiron 1525 (4gig RAM T8100 processor, Vista Home Premium) laptop I've become aware of  numerous problems and decided that I might just need to go back to using a desktop.
 
My main gripe ( along with random fan bursts which slow down performance and random slowing down of metronome count in on recording) is the latency problem - I've got a Edirol UA-1EX usb sound card which according to Sonar 8.5 has a 12ms latency.
 
I use a lot of VST (usually the Cakewalk ones).
I'd like to be able to record 16th notes at 120bpm with out my timing sounding sloppy and having to edit every performance using the mouse.
 
If I go to 6ms, the sound starts to sound metallic sounding, even though the CPU never goes above 40% even with another 5+ VSTs running plus other audio tracks with fx.
 
On my 5+ year old AMD Athalon desktop (1.33 Ghz? and 2gig RAM, PCI  Terratec DMX6 fire soundcard running XP ), I don't have a latency problem at all, until I max out the CPU with too many VSTs.
 It feels much more responsive in general too. (Although it can't even run one instance of Dimension Pro, which is why I bought " a high spec laptop" two years ago).
 
So I am back to considering buying a desktop as I'd have a much more responsive system using PCI sound card and a faster mother board.
 
As my projects use about 60% VSTs and 40% loops/audio recordings, would I be better off buying and old an Quad Core system or i3 or i5? Am I after the highest GHz or lower speed and more cores?
 
( I can't justify i7 really, as I get so annoyed/tired of technical  problems I don't make more than 4 tracks a year these days!)
 
Thanks.
 
 
 

As far as clock speed versus number of cores, cores are usually more important. The operative word is "usually", because it depends on the degree of parallelism any particular application achieves.

Fortunately, SONAR is one application that knows what to do with multiple processors/cores. For DAWs, a quad core will usually significantly outperform a dual core even if the latter has a much higher clock rate. VSTs, unfortunately, are typically unable to utilize multiple cores well and some vendors even recommend against multiprocessing.

I cannot comment on the newer processors, since I have none.

EDIT: I see Scott disagrees, offering the opinion that GHz trumps number of cores. He would know. My background is mostly non-DAW applications such as database servers and other boring crap like that. I'll defer to Scott's advice.