I'm 6' 195lbs and selected 800cc, will they be too large and eventually sag? (Photos)

There are volume limits based on anatomy. There is only so much size that a breast envelope can accommodate. Occasionally, in cases where patients are seeking very large volumes, staged expansion may be employed or serial augmentation to gradually develop more space.
That being said, I do caution against pursuing such large implants. The risk of complications increases with volume (with risks beginning to increase after 400-500 cc). Regardless of patient size, 800 cc is a large implant and represents a significant tissue stress (nearly 1 and 3/4 pound per side).
My recommendation is greater communication. There always usually more than 1 option for a given BWD (higher profile greater projection and greater volume). If you are not entirely comfortable with your choice re-open the dialogue with your surgeon.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).
Donovan Rosas MD
Board Certified by the American Board of Plastic Surgery
Member: American Society for Aesthetic Plastic Surgery, American Society of Plastic Surgeons
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Thank you for the question and pictures.  Based on your photographs, I think that you are starting at a good place and should have a very nice outcome with breast augmentation surgery.   I also think that your goal photographs are realistic understanding of course that goal photographs are communication tools not guarantees of exact outcome.It is not necessarily that larger implants are more problematic;  it is that the use of a breast implant  that is TOO  large for a patient's frame can be problematic.  
Generally speaking, every patient undergoing breast augmentation surgery should understand that their anatomic starting point will limit the outcome of breast augmentation surgery.    In other words, a patient's starting anatomy will limit how large of a breast implant can be utilized safely. The use of a larger breast implant (than what is safely "allowed" by the patient's anatomy) can be problematic;  potential problems include breast implant displacement/malpostion issues ( such as bottoming out, lateral displacement, symmastia...) and/or significant breast implant rippling/palpability. In my practice I have found that taller patients DO end up with larger breast implants (that seem to fit their frames better than smaller breast implants would),  when it comes to achieving a proportionate look.
 The best online advice I can give to ladies who are considering breast augmentation surgery is:
1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you're looking for. Ask to see lots of examples of his/her work.

2. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining breast implant size/type/profile will most likely help achieve your goals.
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or “D or DD cup” etc means different things to different people and therefore prove unhelpful.
 Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup size may also be inaccurate.

3. Once you feel you have communicated your goals clearly, allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals. Again, in my practice, this decision is usually made during surgery.
I hope this helps.