I'm exactly 6" around mid-shaft, 6 3/4" around the base and was my wife's first. It took us multiple attempts over a period of days before we completed the act. That particular part of it was not at all fun, to be honest. It continued to be difficult for a while after that, and according to her, it was at least a little uncomfortable for a couple of months.
After that, things have been great and she loves my size. The only accommodations we make now are 1) we rarely go without lube and 2) with rare exception, we start penetration in the missionary position. I haven't pondered the mechanics of why, but it's just an easier entry that way. Otherwise, I can pretty much pound away to my heart's content once we get rolling and only have to be careful when I'm taking her from behind and she's bent at the waist, which is a length issue anyway.
As MR mentioned, UTIs were a problem at first, too. We learned with experience that her cleaning up and peeing shortly afterward takes care of that. She usually cleans up before, too, to be extra safe. That's the one down side of size to me: sex can be such an undertaking. Just grabbing her in the kitchen, ripping her panties off, having a quickie bent over the counter isn't happening. I suppose it does keep me from becoming lazy, though. :wink:
My advice for a 6" girth taking a woman's virginity echoes what others have said about taking it slow, but I'd add that even that said, know that the amount of effort and patience required my still surprise you. Try not to get frustrated if it doesn't work right away.