Depends on the woman Paul mate, not all women need or even like being stretcarbonsmudged and hurt by a big cock, one of my female friends doesn't want huge cock she just wants different cock. Someone new and exciting, it's the idea of fucking with a guy she's not married to that turns her on most. I'm not huge down below, just a bit above average really, but it's plenty for most of the women I've ever been with.
Mind you some women need em big to get anything out of the fucking, my wife needs a good big cock occasionally to stretch her massive holes and make her feel it, mind you Julie likes being hurt during sex it intesifies her orgasm. I'm plenty big enough for her in normal circumstances, but when she fancies being roughed up and hurt we get the big boys in.
Your lady might be ruined by a huge cock and need it again and again, or she might just take any size as they come, or should that be 'cum'

depends on her needs and preferences.
My advice to you is go with the married guy if the wife wants to try this, he's got what she's fascinated by, a big tool, and he's got a wife of his own so won't want to take yours away from you.