I recently had the chance to compare some setups.

KLX250sf completly stock but lowered(gf's bike)
KLX250sf stock suspension with dynojet kit and 2 brothers slip on (not sure if intake was changed at all) stock gearing.
KLX331s with FCR and Muzzy. 14/45gears

I could definatly feel the increased performance between the stock bike and the jet kit with slip on exhaust. Would higly recomend to anyone considering. Jet kit bike had much improved acceleration

The 331 with FCR and Muzzy and 14/45 is a whole different beast Must hold on when you twist the throttle and quickly run out of gears. So my opinion is the 351kit would be well worth the $. Rejetting should go without saying and I also think you want to make some kind of exh improvement even if its just drilling out the stock exh.

Again the Jet kit and slip on made a very considerable upgrade.

 

I did another top-speed run today after work. Not the best of days to try one with the winds blowing at 20~30 mph from the South. But I was going east and west bound. Once again, top speed is 65mph in the upright position. Even thou top speed did not increase, the holding power to stay at speed did. No longer does the engine want to slow down every time I hit an incline. Mid-range power is much improved. Heading South bound in a 20mph wind, doing 40mph in 6th gear, the engine use to struggle and would requite a quick downshift to acclerate. Now after the DynoJet, the engine just pushes along and with a twist of the throttle, start to power through it. Also, no more de-accleration coughing.

Just doing that DynoJet upgrade was a great enchancement. Now I'm itching for more power.

 

Just a re-cap after the DJ kit. I finally been able to ride the KLX again after my hosiptal visist more than 2wks ago. And got some road mileage done. So after installing the DJ kit, TwinAir air filter, and KDX snorkle, I would expect my gas mileage to decrease to some degree. But after 105 miles (94.5 mi w/ a 10% speedo error), I still have not needed to switch to RES yet. So this gives the KLX a range still within 63~70mpg driving under 55mph on paved roads. Now I just need to heal a little more before I abuse the heck out of the throttle going off-roading.

 

maninthesea, that was my 250sf you rode, yes, i am using the kdx200 snorkel.