The first difference you would notice would be the increased bass depth and dynamics. The 205/2 were a little on the lighter and tighter side and while they have good dynamics, they didn't plumb the depths as well. You might have even put them bit closer to walls for boundary reinforcement, which has its own set issues to certain points of in room imaging.
Both speakers are known to have a more forward mid range, but the B&W us definitely tuned to sound a certain way in the mid range. Its intentional and coming from the Kef and its more neutral sound might be to or not to your liking. This is certainly one of the key areas where people like or loathe that B&W sound. I also believe it will take a bit more work to get the B&W to work properly in room with its dispersion characteristics not being as linear as the Kef.
At the treble, the B&W will be somewhat more lively, but also quite refined. A hot recording will so on either speaker, but the B&W might be less forgiving with it having a bit more energy, but its still a very clean transducer so it won't be a fault on the tweeter but simple how the recording was made.
So I would take my top vocal tracks, both male and female, and see you enjoy their house sound. If you go on from there, bring a track you enjoy but also something that might be a bit too enthusiastic in the treble.
The final note is power, which I believe the B&W to be more of a load into lower impedance. The key factor is the demand is in much of the mid range, which also tends to have the highest energy levels. If you under power them, it will likely be more noticed.