what speakers would you choose for a hometheater?

Not knowing the size/dimensions of the room, and equipment associated with driving the speakers, it is difficult to make any suggestions. You say that you have 2 channel already handled, so I assume that you won't use these for music at all except for maybe concert videos? Or will you be listening to SACD Surround/DVD-A 5.1?
My suggestion is spend some time at the dealers listening to the speakers that deliver the most impact. You may find that the CM series or the 600 Series will fill the bill and save you some money in the process.
I think that (of course we don't know yet what you are using or plan to use) that the pre-pro and amplification play a very big part in the delivery of accurate and involving surround sound. From my experience I would rather have the fronts and rears match in size or be very close in size than have bid fronts and small rears. I feel that DTS-MS utilizes the rears more and that I lose bass response in the rear. Also since I listen to SACD/DVD-a 5.1 I would get a more surround envelope that I prefer.
But you may have a different taste that I do. And if you are utilizing 7.1 the the larger rears would probabaly not make sense. Just offering my opinion.

You certainly do not need full size speakers for the rear surrounds.
If you chose 800's for the front, you could easily use 805's for the rear surround,
You could even go for the 7.1 style and have four 801's for the rear sets of surrounds.
If like Theo, you will want a wider frequency response (more bass) then I would say 803 for the rear.
Center channel should be the upper quality dedicated center from B&W.

It's home theater, it doesn't make any difference.

I find that hard to believe that speakers don't mater because they are in a home theater....forums have all kinds of people i guess...

the room is 15 by 25 feet and the electronics could run any of the speakers.