I had an xt660 18 months ago and i did the lot air filter dna stage 1 and 2 ,snorkel mod,02 sensor mod ,fuel mod ,beowolf exhausts. and bike was spot on still cut out from time to time when kicking down a gear but not often. sold that and have just bought 2 xt660 in the last 3 weeks both 2007 plates both almost as new one with 6000 and one with 7500 miles on them one and two owner bikes so not been used much.anyway one is a 2006 model on an 2007 plate and it rides 100% spot on no cutting out nothing and pulls all the way up to 100 mph I am NOT going to add any mods at all to it. why feck with it. the other bike is a 2007 model (02 sensor fitted to headers ) I have cut the snorkel down (inside air box bit) and added a k&n have bought the fuel mod (not fitted yet) and have to by the 02 sensor so i can fit both at same time. my honest opinion if your bike rides spot on with no problems at all I would leave it. the 2006 model bike i have needs nothing doing to it, no surging no cutting out pulls like a train (for an xt660 that is) so why pi** about with it. the 2007 rides grate again no surging or cutting out but feels like it could do with one or two more horses pulls all the way up to 90 mph then just lacks a bit so will put the mods on. PS the other member saying Nitron shocks are good he is right i have one on my FZ1N and my Tiger 800 and my wifes FZ8 you can not beat them for the money. and as i am trade i get a very good deal on them