I actually just swapped belts today from the factory belt, to the SP belt.
I GPS'd my top speed with my factory belt, hitting 63km/hr
After swapping the belt to the SP, I drove the exact same road, same conditions, by myself etc, and I could hit 64-65km/hr.
Mid range and lower end definately a bit 'snappier' I find, if thats the right term to describe it.
Dealer sold me the belt for 67$ Cdn.
My factory belt is exactly 1 year old, and has seen some hard hard life, lots of hills, hard starts, water/mud, towing, and a few times I was sure I was going to smoke it, just by not putting it in low range, surprisingly it was in great shape.