Just thought I would share my recent (rare) four stroke experience... Rode my friend's new 2011 CRF450, and all I can say is that four strokes have certainly changed over the past six years since I last rode one :shocked. I was pushing as hard as I could on my bike (2010 YZ250 with DEP pipe/PC silencer/suspension set up for me) and the bone stock CRF to see if I was faster on one. I was averaging four seconds a lap faster on the CRF, used way less energy and it wasn't even sprung/valved for my weight. However, the fun factor was truly taken away on the 450. Even though I was quite a bit slower on my 250, I only ride for fun these days and the 450 cannot compare to my 250 when it comes to pure riding enjoyment. If I decided to start racing again, I would certainly switch to the 450.