I wrote a detailed comparison on the old forum, pity its gone.... In summary (I still use both)
VX7000: Heads no longer available but are heavy and serviceable in most cases. excellent unit, slow rewind, good recording clarity, has some problems with intergration in newer TV's, good tuner, some support for active only recording (i.e security camera), supports tape electronic labeling.
VX8000: Heads still available, lightweight and easier on components, better recording clarity, software update to 3.1 (STB and other features), slightly better internal tuner, fast rewind, smaller width than VX7000, newer unit, about double the price of the VX7000.
Both support the BL1000 though the VX7000 fits the width of the MX6000.
Beoaus.