Ok I finally succumed to the 4.12 drivers and now the crashes have gone, but I've been getting a weird bug whereby facing certain directions in certain areas makes the whole GUI disappear - the wings, team box, map, inventory, shortcut bar, stats - everything. I still seem able to use the shortcut bar but it's hard to test anything else.
This has only happened in Inferno (very frequently) and the 100% room just before the 25% area in Camelot castle. Any ideas? Oh, and the first person to suggest upgrading the drivers will get slapped.