I did a quick google search and here is a thread discussing the PE of the EQ6.
http://www.cloudynights.com/ubbarchi...l/fpart/2/vc/1
It seems the earlier models had trouble with the reduction gears causing bad PE and later models are better.
There are also upgrades that one can do to them.
I also remember a site at Andy's shotglass astronomy where you can get the worm and gears for an EQ6 coated with some advanced super slippery coating that reduces the PE tremendously.
So my conclusion with little data would be that they can be made to be good but don't expect them to be perfect out of the box. But there is an upgrade path if you don't mind the fiddle and wait approach.
But my warning to you would be that the most important part of your imaging system is the mount. You get some weakness there and you will never get an image past a certain standard. Plus you will be chasing what is causing eggy stars and that will make the whole hobby unappealling and annoying.
Hell, I've got a PME and I am still spending time chasing mildly eggy stars at 3 metres focal length sometimes. Its a matter of setting it up and I will get there as I had it earlier before "I improved it" hehehe.
Greg.