I edit with both, and I will always prefer PPro. Both systems are stable for me, but I think a stable PPro is a result of a stable computer. I’ve had my PC crash just as much as the Mac.
FCP and PPro are very similar, so you shouldn’t have that tough a time going from one to the other. I think PPro is far better to work with, and the integration with the other applications make editing easier.
Motion is nice, but it’s no After Effects.
If your only problem is stability, then in my opinion, I’d stick with PPRo, and just upgrade your computer. I use PPro all the time, and it’s rock solid for me. For what it’ll cost you to get a Mac with all the software, you could easily get a new Dell or HP workstation that’s really powerful and keep the software that you have. If you’re not using the current versions of PPro and the rest, I would really recommend upgrading.