I went from 37 -> 40 -> 50 -> 60. 40 -> 50 was noticeable. 50 -> 60 not so much, at the same viewing distance. Until I saw my old 50" in my mothers living room, and it felt like a 32" set. When I used to see some of my friends 60" sets I thought it was huge, but when you look at one for a few days you get used to it pretty quick. Part of it might be because the bezel is fairly thin and the stands are much lower these days. 42 -> 55 is a significant leap, but dont expect to be impressed with that size for long. It would be a good upgrade at your viewing distance, but I'm at around 10' and feel a 65" or 70" would be about right.
email@example.comGhz * 16GB RAM * Gigabyte GTX 780 Ti OC 3GB * 840 Pro 512GB * 24" Asus VG248QE 144Hz
Mac Pro 2 x X5690@3.4Ghz * 16GB RAM * Gigabyte R9 280x 3GB (EFI) * 840 500GB * 27" Dell U2711
Mac Mini i7 2.6Ghz * 16GB RAM * 850 Pro 512GB * 27" Dell U2711