Actually D300 is faster at 6fps in 12mp mode (where as the D2x is "only" 5 FPS). The D300s is even faster @ 7fps. Both D300 and D300s can go to 8FPS with the grip and correct batteries, whereas the D2x is still only 5fps. It can go faster in crop mode up to 8fps) but only at around 7mp resolution.
D300 also has built in flash, commander mode and a MUCH better LCD screen to boot to name but a few. The only area where the D2x might best the D300 is at native ISO which is ISO100 vs the D300's ISO200.