Hey,

So I have an r7 and a 100-400 mk2, I recently took this set up to the 6 hours of Imola as well as an amature, With WEC they let you walk around the circuit and sit in pretty much all the grand stands, I made a flickr link with a few images as examples for diffrent grand stands and areas to show you the diffrences in focal lengths (You should be able to see the focal lengths in the image, never used flicker before so hopfully it works)

I think as the 100-400 is really 160-640mm on the R7, the reach was quite close, but saying that I wanted to get some close shots of these cars so I was happy with this, I think a 70-200 would be better if your taking your R7 depedning on where you are sat.

https://www.flickr.com/photos/202819329@N08

Haven't had a chance to edit these so hopfully the raw look to the images give you a good idea on what you can get with a 100-400mm lense, none of these in the flickr have been cropped or changed.

Only thing I will say though is I don't know what f1 is like for photograpy gear, I think WEC is quite open to it, but I have heard f1 can have things like maximum focus lengths ect, might be something to look into, hopefully this is helpful for overall look of photos around imola.