To aspiringdd: Welcome, welcome!
I've certainly heard the stories (some worse than others) regarding doctors who are completely inflexible in what size they'll help you get to. I've heard that some even have a really bad attitude. If you meet anyone like this, run, run fast, run far. You don't want to be spending money on this type of surgeon.
You might want to consider travelling to another city for the surgery. There's Vixen's surgeon (I forget which city he's in). Then there's the surgeon in Lake Tahoe. Both surgeons are quite open to helping you get HUGE.
Probably the biggest limitation in size (once you've got the surgeon you want) will be how much skin you have to cover the implants. You don't want to end up in a situation where you have these monster implants and the stitches are straining to keep the wound from popping open. I can imagine some strain, but .... No doubt the right surgeon will give you great advice in this area.
Something you might want to do is start collecting pics of boobs you like the look of. Print them out and bring them to the doc and say "I want to look like this".
I don't recall whether anyone has mentioned this, but one reference site is
www.implantinfo.com. Browse the personal experiences if you like. Pretty informative, and spans quite a wide spectrum.
Even when you've found one good surgeon, see if you can't find one more. See which one is the better communicator, the better listener, the one more likely to give you the warm fuzzies. And make sure they've had an established office there for a while (unlike the horror stories of that travelling unlicensed surgeon, what was his name? Dr. Sanchez or some such?).
Hope some of the above info helps you out.
Jim{ruby}