To IS or not to IS (a canon 70/200 4L thread)

[Hans_Andersson]

I recently bought a tamron 70/200 2.8 wich is supersharp but the AF has some issues with being slow and inaccurate wich leaves alot to be desired for rc and motocross.

So my plan now is to exchange it to a canon 70/200 4L but i have some questions.

Since the tamron and most of my other lenses have 3.5 or less (2.8 is popular with me) i wonder what you guys think about the canon being only 4. Will this be a problem? How is the bokeh on this one?
And since it is "only" 4L im guessing that the model with IS is the one to go with, but the price is really high for me.

Anyone here own anyone of the canons? or maybe have tried both?

And yes i have tried to search but im an idiot with bad engrish so any kind of help would be nice.