I have not heard Merlin speakers, so my input may not directly help the posters question, but I wanted to address one response. Someone said that the S805's don't do old rock and roll and have no real PRaT, I take issue with both these statements. I have no problems with PRaT nor would I expect a company like B&W to send out a speaker, especially from their Signature line, to lack this, just my opinion.
It has been awhile since I have spun some old rock and roll, with exeption to Segar and Elvis a couple times when checking things. This led me to dig out the few r&r cd's I still have and I actually have to thank the poster for making the comments because I heard these better than I have before. Being R&R, would it be more 'fun' with some bigger woofers? Yes, but what it did it did better than I've heard these CD's before, not that these recordings are anything to write home about.
All that said, if B&W speakers aren't for you, so be it, they are for me. Just remember that the more juice you give them, the happier they are.