After Emagic/Apple pulled the rug on us PC users a couple years ago

I have still held out bravely and used Logic 5.5 with no upgrades. Worked fine but I start seeing the limitations now when other software (especially VST's) get upgraded. The new Battery3 and FM8 modules send Logic into an 'infinite loop' - the software becomes non-responsive. I have to believe that his has to do with memory and/or horsepower requirements. Doesn't matter, it's just not really working.
I am now considering to finally jump on the upgrade or crossgrade train. Should I bite the bullet and move over to the Mac and Logic Pro 7? It's a lot of money and would be a major platform shift for me. Then again, I am very familiar with Logic so this might make the transition of my projects very smooth. Haven't looked at all the VST software I own, but I believe that most of it runs on Mac as well as PC. I hope that re-registration is not a problem. It's all within legal use.
Or ... should I stay with my hardware (Athlon64 3200+, 1GB RAM, WinXP) and crossgrade to e.g. Sonar6 or Cubase4. If so, which one of the two? What other options should I consider?
For completeness, I also have a TC Powercore and a UAD-1 DSP card inside the machine that I would like to keep active.
Any advice will be much appreciated,
MisterBlue.