I've been using 2.5s for 7 years and love the heck out of 'em. Currently use a 9 wt 300B amp in a small room (11 x 13.5) and get all the volume I need. They are musical speakers that work well with a wide variety of amps even though they are only 86db efficient. They also have a very stable and easy impedance curve and a very benign crossover phase angle, which two things are as much and maybe more important than efficiency.
I have attempted to sell them a couple of times and just seem to not be able to let go. Just a week ago I ordered a pair of Merlins and have a buyer for the ProAcs but to be honest, I tried to back out of my own deal! I am selling them but they'll be missed but I'm sure the magical Merlins will more than ease my "pain". (And my wife won't let me keep both!) The 2.5s are the definition of smooth and non-fatigueing sound, and neutral in the most enjoyble of musical ways. Check out audioreview.com for lots of opinion on them.
(I understand, from people whose ears I trust, that the Merlins will take that musicality to a whole other level.)