I played both Arcanum and Fallout unpatced and didn't have any problems (I remember... Don't know why I didn't pach Arcanum, but I played Fallout on our old computer, who had a really slow conection...)
Übereil
Troika's not known for technical issues w/ the Engine.
Troika's known for more quest bugs than anything. Some quests are broken and can't be finished w/out the patch.
Also, in FO2, before one of the patch, saves could corrupt on you.
