I have the Kef 3005se hooked to a onkyo tx-sr605 and opted for the 5.1 as my room is 18ft x 12ft it sounds awesome.
I have also some kef Q7 floorstanding speakers and used these as my fronts and bi amped them sounds even better, though i now have 2 kef fronts in my bedroom wrapped up and back in its box, will hold on to them till 7.1 more widely available as not too much on blu ray dvds with 7.1 soundtracks at the moment.
Also you say that your going for the wireless system, im not sure if you know but its the sub thats wireless not the surround speakers also heard the non wireless is much cheaper, just in case you dont know this.
My sub is wired using a QED subwoofer cable, for the sake of 1 cable you may save a good fortune.
As mentioned save the money for the 2 additional speakers and invest in good cables makes all the difference. I have the QED silver Anniversary cable there awesome top rated cable and not that expensive now.
All the best with which ever option you go for.