PJ,
I've heard the 2500, 3500, and HTB2. The 2500 and iQ3 is a fantastic setup. The 3500 does extend a bit lower, but at a bit of a loss of punch. I'm a big fan of the Kef sub: very clean, tight bass. In a smaller room, it should be great. the major downfall of the Kef sub, is a shortfall of amp power. It will probably not vibrate out your nightstand drawer, and spill your condoms on the floor. If you watned it for movies, I'd go elsewhere. But the subs are IMO, great for music.
Smaller room you say? I'd def lean toward the 2500 over the 3500.
The kef mids are WONDERFUL.
I have not heard the iQ1, but I would really look at upping to the iQ3. It isn't much more in cost, but I'd imagine the larger woofer would certainly help the midrange. I loved my Q1(=iQ3), and just wanted a bit more .
Right now I am using my iQ9's with a polk sub. It certainly helps fill out the lower frequencies that the Kef's struggle with in my larger room. however, I am 'in the market' for the PSW3500, sometime in the future. When? Who knows. My lifestyle may change enough that it will not be feasible for MADD BASS IN YO FACE in the next 6 years.
Feel free to contact me, and I'll gladly send you my Q1 for a demo. They are just rear speakers now, and I don't have time for 5.1 movies, lately.