Dangers and Risks of Large Breast Implants?

GIven your description of your frame, I would recommend a smaller sized implant, perhaps in the 400-500 cc range, to give you a dramatic improvement without overstretching your tissues. Once these tissues have been stretched out by very large implants, I think it is difficult to maintain a natural look to your breasts. Also, as you get a little older the tissues will thin, and then if you want to downsize the implants a bit, it will be very difficult to do so without adding the additional scars of a breast lift. If however you decide later on that you want to be a bit fuller, it is easy to do so through your existing incision without adding new ones.
In general, I advise my patients to be a bit more conservative than what you're describing. In the end, however, it's your body and your choice, as long as you and your surgeon have an honest discussion about the pros and cons of the implant choice, and you are willing to accept the possible risks.

Yes, this is a larger than average breast implant.
There are numerous increased risks associated with this, and I am sure I will not even touch on half of them, but consider the following.
The size of the implant has been associated with:

Increased risk of loss of nipple sensation
Increased risk for long term breast ptosis (sagging)
Increased risk for chest wall deformation (curving of the ribs)
Increased risk of rippling or palpable /visible creases
Increased risk of lower pole tissue attenuation (thinning of the tissues of the breast)
Increased risk of secondary revisionary procedures

These are a few of the risks off the top of my head. Please discuss with your surgeon.
Most importantly, remember that although you are seeking breast enlargement, many women present complaining of breast overgrowth desiring breast reduction. These women report limited physical activity, neck/back/shoulder pain, shoulder grooving from bra straps, numbness in the fingers, rashes beneath the breasts, etc.
Many of these women feel significant relief with reductions as small as 300 cc yet you are considering adding twice that to your breasts. Think it over carefully.
I hope this helps.