I love the name Gavin! I don't Looove Vincent, but I like that it's after your father. Plus it is a classic name that is not weird or hard to say. (I feel the same way about DS -his mn is Edward, after my Dad.)
I think it's a very nice name. To not get caught up in the VIN-VIN thing you have to envision a last name and keep in mind that you are not going to call your son Gavin Vincent (except, of course, when he's in trouble!). When saying a person's full name people usually pause briefly between all names.
Re: Middle name?
My thoughts exactly. When the first name ends with the same letter/sound that the middle name begins with, it makes it difficult to pronounce.
This. The first thing I thought of. Vincent Gavin doesn't feel the same.
This. It is a little vin-vin but I like it.