I've had glitches with stock Froyo, so to say that it's default the most stable isn't true. Before I rooted/ROM'd for the first time I used to have some issues with 3G data loss.
Everything still gets patches and fixes, so that doesn't mean a thing. And I have no memory issues with SS5.4 and I don't use any of the tweaks, no Supercharger and no compache. Nothing.
I can without a doubt say that GPA14 and SS5.4 are absolutely stable for me, and I have no doubts they would be just as stable as PE4.2 and Sourcery 2.2. Every phone is different, and perhaps some phones simply can't handle GB as well as others. The OP needs to test out all of his options and make his own decision based on what his phone can handle.