100-400mm zooming stiff?

Hi Folks,

I've been thinking about investing some $$ in an L zoom lens and the 100-400 has been at the top of the list. I checked one out at the store yesterday and found the zooming action to be stiff. This could be good since it's a push-pull zoom (it won't shift focal length without effort), on the other hand it seems like it would interfere with quickly changing FL.

Is there an adjustment for the friction that the sales person didn't know about? Does it loosen up over time? If not, is the friction a really good thing?

I'm going to rent one to check it out further. Your experience would be appreciated.

Another option I've considered would be to buy a 70-200mm and a teleconverter. If I did this it seems like the f2.8 would be the only option, due to losing a stop with the converter. Again, I'd appreciate any wisdom from y'all.

Thanks!