I'm with Tweed. The Cary amps combined with the Response 2.5's is a wonderful match, and will provide a warm, lively, and very musical sound. The B&W's, especially with ML amps (a better match than Cary IMO), will produce a sound with greater speed and definition, but for me is a little bit too dry. Its all a matter of taste, and your ears will be the best judge of what sounds good to you.
A word of caution though - the 2.5's are not terribly efficient speakers, and the smaller Cary amps (SET's) will likely have some trouble driving them. I'd stick with the PP amps with these speakers.
As for your other question, I find that there's quite a difference between the Studio and Response series speakers. The Response speakers produce a fullness, soundstage, and midrange clarity that is unmatched by the Studios. I think that youd find a dramatic, and wholly positive improvement by upgrading.
From a personal standpoint, I've been using ProAc 2.5's with CJ amps for several years and have been very happy with the sound.
Good luck,
Ken