As a reference, I like howlongismyschlong.com just because it’s an easy site to enter data and get a summarized result plus it links to the three studies that it uses. Based on that site, average girth is 4.75” (or perhaps closer to 4.875” if we look at medians rather than average of the three studies). I don’t know if these studies are considered reputable or not, but the data seems reasonably consistent with other sources.
IMHO, ideal girth is probably around 5.5” (90th percentile) for regular vaginal pleasure. I know my wife has become much more effusive in her unsolicited praise of my penis as I’ve gotten bigger and there’s also been an occasional reference to being a little rougher than normal some nights and a urinary tract infection or two. However, she’s pretty small down there so if she really likes 5.5” then perhaps 5.75” is an even better, generally speaking.
I think when you get to 6”+ MEG, the “jaw dropping” literally has to happen for her to get her mouth open wide enough to give a BJ without teeth.
11/20/2011: BPEL: 6", MEG: 4.75" (goal BPEL: ~7", MEG: 5.25")
5/9/12: BPEL: 6.5", MEG 5" (goal BPEL: 7.25", MEG: 5.5")
3/5/13: BPEL: 6.875", MEG 5 5" (max goal BPEL: 7.5", MEG: 5.75")