From VGA Charts:
Radeon X700 XT RV410 128MB DX 9.0b 475 1050 128-bit 8
Radeon X700 Pro RV410 128MB DX 9.0b 425 860 128-bit 8
860 MHz advertised usually means = 430 MHz (DDR)
Your Video RAM is running at the correct speed for a Radeon X700 Pro.
I think you are confusing it with the X700 (vanilla / non-Pro).
Still, only 128 bit wide video memory, so don't expect miracle performance.
As in: 430 DDR x 128 bit = 13.76 GB/sec
vs say: 475 DDR x 256 bit = 30.4 GB/sec (like most Radeon X800 and GeForce 6800 cards).
Your card looks OK to me (spec wise).