The KEF R300's only weakish point is low bass. They put out energy there, but it doesn't have that last word in resolution (It is a bookshelf after all, I doubt any bookshelf with a 6.5" driver can do low bass with fantastic resolution).
I had chance to hear the R500s and they do it just slightly better, but not a huge difference. I've fully integrated my R300s with a R400B subwoofer.. This set up now does low bass INCREDIBLY well. I've retired the 12" and 10" subs I had in my room now. The bass lines are incredibly well defined due to the lack of ports (I bunged the ports on my R300). I'm of the opinion now that ports give you the weight and sound of bass, but they don't give you the same definition as drivers do. Even the bass Thay my 12" sub had was woolly, as it is ported. I'm sure there are ported designs out there that can do resolution but I'm sure they are of the far more expensive design than I was using with my previous sub.
As for the rest of the sound I haven't heard anything with more balance, more clarity and more resolution... that sounds as clean as these speakers do. I think it's a great bookshelf as it is 3 way design due to the extra room on the face thanks to the UNI-Q, and so the midrange and bass drivers aren't working too hard trying to cover too much of the frequency range like they do in other designs. If you combine this with the R400b subwoofer which is a dual 9" driver force canceling design, this combo works very well indeed as a 4 way system. There is almost zero cabinet vibrations on anything (I can't feel a thing when I put my hand on either the speaker or sub).
All in all I have a giant smile on my face every time I listen to these, I'd say if you had the room and the money to get the R500s... you should get those and down the line add in the R400b, I'd be willing to bet this combo is a little better than the R300s with the sub and better than the more expensive R900s without the sub. (I've not heard the R900s so it's a guess) But what I read is the R500s image the best out of that range due to the very narrow cabinet and I think they might give a bit better dynamic range over the r300s due to the larger cabinet and I know first hand the sub gives you some terrific low end. The R300s do throw a massive soundstage and image very well indeed. I can't comment on the Wharfedales.
