If you're thinking about deep sky imaging Adam, you'll almost certainly need a 2nd scope for guiding, 2nd camera, a bunch of wires, dew covers, DSLR or CCD camera. When you add up the weight of that lot to your planned 8" OTA you're getting into 12-13 kg area. HEQ5 can do it (just), but many say EQ6 gives you more room to grow in the future if you can afford it.
EQ6 and HEQ5 have better gears and better stepper motor sensitivity and guide port.
Astrophotography can be a bit like banging your head against a brick wall for fun sometimes. You really don't want to be working past 1/2 or 2/3 rated weight of mount or it all just gets too off-putting.
For visual or planetary (video) work EQ5 should be fine though.