Mine was reported as 93-97cc on different scans, on the larger side, but nowhere near a record. It wasn't giving me any BPH side effects, even though it was pressing quite a large dent into the bottom of the bladder which could be seen on my flexible cystoscopy.
We recently had someone with a 600cc prostate in a local support group, which had only just started causing symptoms. That's the largest I've heard of. (They had BPH, but not prostate cancer.) While enlarged prostates do cause increasing symptoms as they get larger, there's an enormous variation in the point at which symptoms start, and sometimes they never occur.
I follow one of the well-known surgeons on Twitter, and he used to post pictures of interesting prostates he's just removed and one notable one was 200cc, which is regarded as a whopper.
Enlarged prostates are very slightly less likely to get prostate cancer.