Hello,
I think you all have made good points here. I'll do the try before you buy rental, and there will always be more for sale. I was surprised at the final eBay price of the copy I was watching: UV (2007), looked and stated pristine, including Wimberly sidekick: $5150.
I use to own the 100-400, but sold it because I wanted a faster, sharper lens solution. All crystal balls envision an updated model of that lens for this year. Just like last year. And the year before that. I still want f/2.8, unless my rental experience shows me that I can't carry one.
Cheers, Ralph