A pumper carb will give you that "get up and go" you're looking for, you'll get a snappy jolt of power every time you twist the throttle. The down side is they're not cheap. It is a good value though, $500 worth of engine mods won't get you half that kind of performance. If cost is not your limiting factor, spring for the FCR. If like most of us your looking for the most bang for your buck, the TM40 is your carb. And don't let anyone give you any shit for choosing an XR for woods riding. Scott Summers won 5 GNCC championships on the XR600R in the woods of the east coast.