i've rode on dunlop sp's and kumho's and I like the kumho's better...I heard the breaking point on the kumho's is 400hps but other than that they are a great tire. I also heard they are good autox tires as well. If your a serious autoxer than you should get the g-force.
There is a tuning company in the states that does supercharger kits for porsches and they say the kumho's are very similar to the big buck tires performance wise.
and the best part is their cheap!!