I have an 8" Dob which I am planning to upgrade for photographic use, but I will be going for the EQ6 for the mount, a little overkill but it's stability and accuracy that you want. With an autoguider on the side the EQ6 can be a very useful tool, as long as it's the skyscan version, if not the EQ6 will need to be modified.
I like the idea of getting the Dob (over 8") and saving for the mount later, then do the conversion when needed, you could easily adapt the two mounts so you can use both.
The Bintel 12" Dob is selling for around $998 I think, not bad price for apature you are getting. I think the EQ6 can handle that, weighs less than 25kg doesn't it?
Anyway follow these guys advise they seem to know what they are talking about
In the end it's your decision.