Chris,
I put the SP belt on my 500 6x6 years ago and noticed a difference at first, quicker engagment. But as time went by I either got used to it, or (I suspect) the belt wore into shape after some use and it seems to be back to stock now. Either way I think the SP belt was a good choice because of the different design and it was a little more heavy duty. I have 120 hours on the new belt and no troubles yet.