Do you get random events when just maging?
Cuz if you don't, a friend of mine had an awesome idea. You could get a million bajillion mind runes or maybe some chaos, and get an autocasting staff. Go to some high level NPC where you can safely hide and mage it without getting hurt. Use a low level combat spell on autocast, and since it really won't do damage, you could keep on casting forever, as long as you had the runes. It might be slow XP, but you could go AFK and it would keep going

. Course you might get a random event so jf;laksdjgfla.