I've installed a Delkevic SS70 slip-on exhaust on my 650 Versys .Immediately noticeable the aftermarket muffler resulted in about 7 lbs of weight savings. Exhaust note is deeper almost similar to an open pipe. The Go Pro audio gain dulls this example above 80 kph. On the whole a bit of low end torque is sacrificed. I can't say there's any abundance of extra power but the mid and upper rev range is peppier. Currently I do have the db killer installed otherwise it would be just too loud as there is no exhaust packing within the baffle. My take is it sounds good in the mid to upper rpm range and a bit tinny at around town speeds. A good trade off all in all.