It started happening after following:
-removal of NVIDIA Nforce gigabit ethernet from a bridge with the Realtek Wireless (sharing internet to a wireless-incapable desktop nearby) which means that it was using the router's DHCP and settings (ie netbios?) previously
-heavy file transfers at >12% gigabit utilization (to aforementioned desktop)
... now continues to happen even if nearly nothing is going on, though it can be aggravated by doing an rsync or something heavy over the Nvidia gigabit.
Memtest passed for a few hours, 8gb, so that was only a few passes. Windows mem diagnostic passed. Was prime 95 stable a while ago. (NO OC). It plays Battlefield Bad Company 2 for hours, without hiccup. Past experience with bad memory is that it would certainly show up under that stress.
Worried it might be hardware. Minidumps attached.