I have 500cc implants and looking to go bigger. I'm thinking of 800-1000cc. Is this too big? (Photo)

Thank you for the question and picture. You will find that online consultants will not be able to provide you with specific advice in regards to selection of specific breast implant size/profile to achieve your goals. Ultimately, careful communication of your goals will be critical.
Generally speaking, the best online advice I can give to ladies who are considering revisionary breast augmentation surgery (regarding breast implant size/profile selection) 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 are 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” or "too big" etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on 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 ( after the use of temporary intraoperative sizers). Viewing the patient's chest wall in the upright and supine positions, with temporary sizes in place, help select the best breast implant size/profile for the specific patient.
I hope this, and the attached link (dedicated to larger breast augmentation surgery concerns), helps. Best wishes.

Implant sizes whether too big or too small can be very subjective. 500cc is already fairly large but obviously you don't think it is big enough. The larger you go your skin needs to stretch and will thin to some degree. 800cc is the largest silicone implant so I'm assuming you are considering saline. You will likely see more rippling as the skin and breast tissue thin with time. Feel free to come in for a consultation for further recommendations. Best of luck.