I will have to agree with Calibos and what he wrote about 12" and 16" dobs, he wrote:
"That said, I am not expecting to be blown away by the move from 12-16in. Got my first look through a 20in a few weeks ago and while initially I thought WOW when I went back to my heavily modded albeit standard Orion Mirrored Orion XT12i and looked at the same objects through the same eyepiece, what I thought were new details revealed by the 20in were in fact there in my 12inch scope. I just hadn't noticed them before."
Just a couple a weeks ago I had a chance to compare my 12" Bintel Dob with friends Meade 16" Light Bridge and I was not blown away
Mind you, 16" was better but just not that better that I would spend another $1500 for it. In my opinion that money would be better spent in buying couple of good quality eyepieces.
This is just my opinion regarding 12" and 16" dobs.