It would be helpful if you could narrow it down to at least one problematic mode, though I freely admit that that could be sort of tedious.
Just my $0.02, to narrow down the guilty hack/mode, I find this useful:while true ; do xscreensaver-command -next ; sleep 3 ; ps lax > /var/tmp/lastscreensaverhack ; sleep 57 ; done
And leave it until it crashes, check /var/tmp/lastscreensaverhack afterwards. Maybe xscreensaver-command -watch can be handy too.
Myself, I have the "bumps" mode crashing the xserver, but I am not sure who to blame for it. Right now I am running xserver-xfree86-dri-trunk and savage snapshots, however I think it was crashing when I used the stock 4.3.0.dfsg.1-4 also.
Tormod