I went through a similar process last year. I felt the need for more mid-bass in my system, which meant some larger woofers. I had an upper limit on center size, and agreed with both your wife & mine that the ideal speaker should be unobtrusive.
Centers & mains need to match, so I started a list of speakers in my price range, sorted it by center size, and limited my search to what would fit. (I also had to wall mount, so also limited it to sealed or front ported.) After listening to what was available, I cut up some cardboard boxes & made shapes the size of the speakers I was looking at, to show my wife what they'd look like in our home. I explained that we had to have larger speakers to get better sound, that the best would have 8" woofers, & that the 6.5" pair would still do a good job & be smaller & less expensive that the 8".
If you want to stay with Infinity, I think you should push for the Beta 20's, but you don't have limit your search to that brand. Timber matching across the front is important, but less so for surround sound.
