I run a 10" dob on a eq6 and let me tell you straight away even though a eq6 will hold it and you "CAN" get decent images out of it its a very very big mission and 9 times out of 10 you will be dissapointed with what you capture for astro photography.
i have tuned the guts out of my eq6 fabricated 25mm thick saddle plates reinforced the hell out of my rings pretty much i have made everthing capable of holding way more than they are and where the EQ6 falls down is it phiscally cannot hold the weight from swinging around my mount has no decernable back lash, yet if i tap the counter weight the ota wobbles, thats just from a small tap. Presently im running a ed 80 with a modified finder -->guider and in heavy wind i still have round stars i get great results all the time.
If you have a dead still night and your seeing is great then the eq6 can point the ota and make sure it stays on target, if you have a really light breeze thats constant the eq6 can give you a 50-75% return for good images, anything much more than about 5km/h breeze game over.
i think the saying goes, "you can only squeeze a lemon for juice so much..."
If your keen to run such large scopes for imaging have you looked at the servo cat/argo navis with a field de rotator? i havn't done any research but thats your tracking/pointing ability and you can run some serious kit with those things that can be adapted to biger/alternitive ota's