I think it would be beneficial if you discovered the root causes of the major problems you're having before you dump some cash on a new box.
What OS are you currently running?
+1
if you undersand the choke point you'll make a better decision
Generally speaking
Track count is tied to drive speeds write for recording tracks and read for playback
Sample based synths require RAM to preload samples for timely playback when you hit a key or drumpad
VST plugs and synths which heavilly process sound are doing a lot of calcualtions and so are CPU dependent
Big Hint: Look at the specs and components used by companies whose business it is to make recording computers. They know what WORKS ('cause otherwise they're out of business...)
another +1
Dont worry too much about CPU performance specs. A super fast CPU doesn't necessarily make a good audio machine in of itself and quite frankly, any recent dual or quad CPU is more than likely to be more power than anyone actually needs, and when you get into the realms of the i7 9 series that's crazy power. There's the argument of future proofing but on the otherhand by the time software actually needs 4 cores with hyperthreading to run, the i7 will be obsolete and far more powerful options will be available far more cheaply (Actually right now a lot of software can't take advantages of the i7 hyperthreading and some are finding turning that functionality off makes things run better). So don't worry if you can't save enough for the latest powerhouse CPU right now. And finally, processing overhead doesn't make the slightest difference to recording quality so having a mighty CPU running at 15% capacity will make absolutley no difference to your sound versus a more average CPU running at 35% capacity
Stability and compatability are much more important. Good Motherboard and chipset/FW chipset choices, good RAM latency/reliability, relaible high efficiency power supply combined with the right drives and CPU will make a good audio machine
My own priority list would be
1) Motherboard, avoinding anything with nforce southbridge. Look for passive cooled north/southbridges for quieter operation a proven track record of reliability and compatability across a broad range of outboard gear, Texas instruements FW and PCI options for future expandability
2) Power Supply. Reject anything with an effeciency rating stated below 85% (I would look for better than that but thats the bare minimum) lower efficiencies will not deliver power smoothly under load and cause all kinds of problems from dropouts and system lockups to BSODs
3) RAM (especially for a heavy sample user) good latencies good bandwidth, proven track record of reliability (RAM can fail suddenly with no warning at all)
4) CPU get enough for your current need and near term needs. If you are expecting to make a radical change in VST/VSTi use plan that into your purchase
5) Drives 1 for OS & Apps 1 more for recording
6) Case and cooling go for options designed for quiet cooling and noise damping properties