Size mainly matters to men. From a woman’s perspective average is better, especially adding extras.
I'll admit it, When you're kind of below average it gets into you head. Now I haven't had any complaints butttt...
Me and my wife have regular fun with my best friend. He's much bigger than me. I was a bit taken back at first and after the shyness wore off I could tell she was more into him than me but the nostalgia wares off eventually and now its the best thing we have done together.
In my experience she was very excited, she had only been with guys with average size. She actually thought I was kind of big due to a little above average girth. I would have to say she seemed to enjoy the sex a great deal, she had multiple orgasms. She told me later it was the visual and the different feeling inside her coupled with the fact I was watching her fuck. She did tell me if it was okay with me she would like to continue having him over occasionally.
If I were in a MFM sex scene I want the other guy to have a normal or smaller cock no bigger than5 inches. That is the size I'd like to suck on.