Thanks for all the replies guys.
I hear what your saying Matt, The reason I can't swap front for backs is that one of my back wheels is ever so slightly buckled and I can feel it through the steering wheel when it's on the front. Also the spare is completely buckled!
I'm getting all 5 wheels Refurbed and un-buckled in the summer so that will sort it then and i'll be able to swap them round as much as i like. I was just surprised that the backs wore so differently to the front. As for WIM, I'm there on Saturday, I was only there 9 months ago when I bought the tyres but my mate is taking his IS300 so I thought I'd tag along and get mine done to see how much it's out by after only 9 months.