The slowest X2 is the 3800+ which is equal to (or faster than) a 3.8GHz Intel. The 3800+ runs at 2.0GHz, but performs as good or better than the faster GHz Intel.
Athlon 64 x2 3800+ is about equal in performance to the Pentium D 840 and maybe the 940 except the 940 is on a 65nm and not 90nm and has doubled the caches.
