520 EXC Reliability

Hi chaps, I wonder if anyone can give me any feedback on reliability issues with the KTM520 EXC. I have one on order but am a little concerned about KTM' warning about riding this bike on Tarmac. I live in the UK, and as we dont have very much land to ride on near my home, I do a fair mileage on the road going from trail to trail. I currently own a WR400F which has given no rouble at all after over 4000km of tail and road use. however KTM say that the 520 is a competition bike ( Which I fully understand - but so is the WR400F ) and as such should not be ridden on tarmac as the gearbox is not strong enough, and also the engine needs rebuilding every 100 hours use. Are they just covering themselves, or has anyone had problems with reliability on thier 520EXC.
Do any of you use yours on the street ?
Thanks in anticipation of you answers.

Andy Baker:think