I take it that this is an "out of the box" kernel, and not one you`ve recompiled specifically for that machine?
And your glibc/x11 packages seem to be concurrent, so I can`t see them raising issues with each other.
Any over-zealous monitoring software in the background? (Beginning to clutch at straws).
Ok, the kernel is custom compiled, but it's a straightforward config (just the stuff needed, nothing not, and yes, I've been tracking and compiling kernels for 10 years, so the preceding statement might[*] not be idiotic arrogance).
No software monitoring on this machine. It's a workstation and I'm the sole user, so quotas and what-have-you are all wastes of cycles.
Also, my Slackware 13.1 DVD just arrived today, so I'm going to upgrade my system. I've got a spare partition sitting around which I can install a small 32-bit root partition on, so I can try booting up in pure 32-bit mode. This might take a little while to get completely setup, but I think we're out of straws. (I'm also going to try everything with the stock kernels instead of doing my normal immediate custom compile.)
[*] for definitions of 'might' meaning 'has an extremely small chance to'