With the sizes being that close (6 or 7 inches), I would stay with the same size. I don't think that the size is enough of a difference to look right. IMO, I've found that things need at least 2-3 inches difference to make it look deliberate rather than just that someone ran out of something and came up with the next closest thing.

I agree with Andrea.

The only place I used a different-sized pull was on a very small drawer (9" wide); that one got a 3.5" pull, while the rest were 5". I did put 2 pulls on a 34" drawer.

My drawers are 16", 24", and 27" and my pulls are all 5 1/2". I also have it on my 13" trash pull-out.