Canon 500mm f4 L USM

[robbins.photo]

Okay so a local camera shop is bringing in this lens for me to view from one of their larger stores. It's used but their rating on it is 8/10. Same rating that my 400mm f5.6 had and it's only flaw was a 1/2 cm paint chip. I have the funds to spend on this. If I purchase this I will be keeping the 400mm for longer hikes and for my son to use.

So background out of the way. My question is for those that have used the version one of this lens.
1. Is the clarity of this at least on par with my current 400mm or (hopefully) a bit better?
2. Are there any cons to owning this lens? I know about the weight difference and have no issue with that.

Thanks for taking the time to read.

You use a lens that has a chip missing in the paint?

What in the H-E-Double hockey sticks are you thinking?

Lol