As above, I've had 3 PR3 rears and minimum has been 15000 miles- that's with similar use to yourself, motorway riding/ commuting / well, travelling the country!
In the wet they truly are inspiring, although I believe reports put Metzelers as doing better, but that would be on a track at higher lean angles than we will do on the roads!
PR3's are worth the extra £'s!
I'm a bit of a test monkey though as I do like to try new things (I'm not talking ball gags and latex FYI) currently I have the new Bridgestone T30 and have only done a couple of thousand miles so far so cannot confirm mileage life yet!
Front tyres I've always been happy to mix as I prefer a 'grippier' front, S20 was last one and lasted 9-10,000 miles, which for me wasn't enough, buuuut, it was a very very nice grippy tyre!