I own T45/C40/B25/LR1, my family room is 14' x 17' with 12' ceiling. When I auditioned the T45 and T55, found that the sound was almost equal with the T45 being more detailed and nicer sounding that the T55. I found the T55 somewhat "muddied" compared to the T45. Also the HZ difference in the lower frequency is only 3 HZ, to me it wasn't worth spending the extra cash on the T55. My receiver is a Marantz SR-5001. The T45's more than fill the room with clear sound, so does the C40. The B25's sounded so good that never saw the daylight as rears, they ended up as main speakers for a music only system in my living room. The LR1's were purchased for rear duty, replacing the B25's. I don't hear surround music, so the LR1 do a great job for movies at only $139.00/pair.
I bought my system from Saturday Audio, excellent people to work with.
My recommendation is to go with the T45, and with the money saved consider a good sub, or buying the center (if using the speakers for HT). For sub I got an HSU VTF2-MKIII, but for music sometimes I don't use it as the T45 provides good bass for some type of music, like jazz.