I used to use an 8" newt on an EQ5 for imaging.
It's too heavy. It didn't work for longer than 13 secs.
EQ5 can carry 10 kg for visual. Half that load is recommended for astrophotography.
My 8" did weigh 8kg I think, it's a long time ago. Carbon would still be ~7.3kg - too heavy for an EQ5.
Understandable that you want to keep your trustworthy mount.
Some 6" newts weigh under 5kg, and more newts at 4" = 130mm.
Add the weight of the finder, your camera and this and that... 6" could work
But it definitely would work with an HEQ5.
Or you can get one of those cool cameras that produce
such detailed images with only 1 sec exposure !!! (x2000) - then you can get away with bad tracking of an 8" on an EQ5
(Discussion of this new ZWO camera here:
http://www.iceinspace.com.au/forum/s...d.php?t=144427 )