I had KU31's when i had my mk2 and they were like cheese. Grip was reasonable but they wore out in around 9 minutes. 
Had the same results when I have used them. My tyre fitter gets huge discounts being the regional supplier of Kuhmo, so I pay next to nothing for them. But I prefer to pay a bit extra for a higher spec tyre and last twice as long.
I have conti sp3 on the back of the 135i, they get tortured with the amount of power/torque put through them but even after 6 months and 9k miles I still have 6.8mm of tread (standard 8mm). My last set of Kumhos lasted 1/2 that milage with a far less powerfull car.
