My gains pale in comparison with those of other gentlemen out there. Remember, I stopped trying to gain size once I reached my goals.
The largest gain I've read about was 5.7 inches in length using a combination of surgery and extender work. This was done under the supervision of Dr. Jorn Ege Siana, specialist in general and plastic surgery, and creator of the "Jes-Extender".
There's "BIB" who created the BIB Hanger device who claims to have added 4 3/4 inches in length and 1 3/4 inches in girth over the course of 3 years. I did an interview with him several years back- read here (post #3).
One client of mine claims to have added more than 4 inches in length in 8 months.
There are also quite a few before and after pics of gentlemen who have added 2+ inches here.
I added 1.5-2 inches and wont stop until I reach 3.5-4 inches. It depends how much dedication you want to put in it. And most people reach a goald and stop OR just move on for many reasons.
About 3 months of intensive PE and stamina work. I didn't know nearly as much about PE then as I do now, and I'm amazed and thankful that I didn't hurt myself with the intensity of my work. It did convince me that regularly increasing intensity is very important if you want to force gains.
For maximum gains, my advice would be to start with moderate tension and work up to the point to where the strain is slightly uncomfortable but not painful. If you feel any pain whatsoever stop and assess any possible damage. If you're ok, repeat at reduced intensity.