Clearance is tight, just like the press release photos were showing. Here is another pic, after I jammed a pen in there:
the stock tires are quite big, I guess more of a DH tire. You could easily put some smaller tires on get more clearance if you needed it.
Its tight, but I have yet to see whether or not it will be a problem in sticky mud, it hasnt rained here in NW Oregon for about a week, so when I go out riding this friday, I may not encounter that much mud. But i will aim for all the mud bogs I find
I have never ridden any of the other forks you mention, my last fork was a Fox F80RLC and the one before that was a cannondale lefty (flexy!). the fox was a good fork, But in my opinion, the E150 is in another ballpark and the two were not designed for the same type of riding. The E150 feels absolutely superb, the travel is long and plush, and it is stiff!
I notice no problems with the headset or fork, no clunks, no rattles, everything is perfect. After my first real ride this friday, I will report back with any issues, but at this point, I dont think there will be any.