You might want to look at this thread.
I owned Response 2.5's a few years ago and now have SHL5's. The D series of ProAcs is supposed to be a bit different, so I can't offer a direct comparison. But between the two I do know, I would say that the Harbeth's offer greater clarity, detail, and resolution overall, while the ProAcs have their own special brand of midrange magic, which I always found very appealing even as I longed for greater clarity. The ProAcs may be more dynamic and better-suited to Big music.
I owned Response 2.5's a few years ago and now have SHL5's. The D series of ProAcs is supposed to be a bit different, so I can't offer a direct comparison. But between the two I do know, I would say that the Harbeth's offer greater clarity, detail, and resolution overall, while the ProAcs have their own special brand of midrange magic, which I always found very appealing even as I longed for greater clarity. The ProAcs may be more dynamic and better-suited to Big music.