It really comes down to what you most want to do. Once you get above 8" in any scope weight makes tracking difficulty and expense exponentially more difficult. With modern DSLRs and CCDs you don't really need huge aperture. Just look at the sublime work people show with Takahashi FSQ106s (4 inch scopes).
You can do planetary video work with a dob (Mike Salway has a great article in the Resources area of this site), but its quite a bit of work.
If you're likely to be wanting to do long exposure at any time, definitely worth investing in the best mount you can afford and spending around half that again on your OTA (and then expect to spend 5 to 100 times that over the coming years as you slip deeper into the imaging black hole.....

)
Why not get some experience with a good mount and much smaller OTA to start with? (apologies if you've already got lots of imaging experience under your belt)