I'm a happy X1b user too. The song I just put out that I've been working on since December, I did 90% of it since the 'b' patch was released. It's been working great for me except for that pesky little interleave problem, but that's easily worked around.
Crashing is one thing I never ran in to that was related to X1. It was always something with my Fast Track Ultra, and I got that resolved too by using the latest beta driver and running it off USB power. They just released an official driver for it, but I'm not going to use it because it's working perfectly now and I don't want to risk screwing it up.
Let me give you an example of how well my system is running with X1b ...
My last project (the one in my sig) was 39 tracks. 6 instances of Guitar Rig, 8 of the PX-64 strip, Sonitus on almost every track, some tracks it was on multiple times, Pro Channel enabled on every track, chorus effects, delay effects, Channel Tool, Sonitus reverb, sonitus comp, 3 synths, plus 5 buses with the Pro Channel, Sonitus EQ, Sonitus multicompressor, and I was still able to record solo's with full guitar rig effects with no noticeable latency. That is impressive imho. On an i5 with 4Gb ram with ASIO set at 128 samples and 2 HDD's ... come on, what more do you want? Oh, yeah, V-vocal on the vocal track too, not frozen or bounced.
As much as I love 8.5.3, I never would have been able to do that without freezing tracks. In the future I'll freeze tracks anyway in X1b, just for the sake of not taxing my CPU, but I really wanted to beat the daylights out of it with this project just to see if I could break it and I couldn't.
I'm more than happy.