Oh my giddy aunt.
Ok, in the end I went for an i5-2500K purely because (if I want) it can be overclocked further than the ivybridge 3570 with a good old fashioned air-cooled set-up. I also picked up the board as detailed above.
Having set the whole thing up (twice - the first attempt was fubar) I tentatively pushed the auto-overclock button in the windows application - it asked me whether I wanted 'fast' or 'extreme' settings. I opted for 'fast' on the basis that I didn't know if the kit would manage 'extreme' overclocking. The whole thing went away and thought for a bit before restarting the machine and once I was back into windows presented me with the information that the CPU was now clocking at over 4.3GHz!!! More than 1GHz faster than the stock clock speed!!!
Man, that's frickin' awesome!
Jabo