C.D...Good points in general but in these times, with interest rates near zero, there's very little investment opportunity cost, which lessens your point. If I have $10k laying around earning .10%, why not buy a used mint 400 2.8ii for $10k, use it for two or three years, and then sell it for at least $9.5k. (as long as I've taken care of it)
If you buy a gently used great white, take care of it, and sell it in 10 years, you will have lost only a little money. renting a 400mm 2.8 a few times a year for 10 years would probably cost you at least $6-7k over the years, AND you don't get the enjoyment of owning the lens!
just trying to point out a different perspective.
take care, north
I'm on board with buying over renting. Generally I either find really good deals on new gear... or I buy like new used gear at a discount. So when I eventually grow bored with the gear, I sell it and don't lose much money... but more often than not, I make money.
Though I do entirely agree with trying out a lens in store to see if it is awkward.