Your cache will crap out 1st. You need to get faster SRAMS than 70ns. Digi-key has 600mil to 300mil socket adapters, you'll want to install those first since you won't find much faster SRAMS in 600mil. Next pick up some 15-20ns SRAMS (preferably Japaneese). Make sure everything works at stock speed before you try the fast XTALs. - Paul