Are you going to "probably considerig to buy it in the very far future", Rover? 
The very few people who can afford and are willing to carry this kind of optics will most likely rent one and the decide if it suits their needs. I think it's hard to make a rig stable enough to test these things - and the usual test parameters might be useless if it has a) slow AF or b) issues with WR or c) can't take a bump.
Roie Galitz took the new Nikon 500/5.6 PF with him to Kamtchatka to compare it with his 500/4. See also https://www.dpreview.com/articles/388997...-kamchatka
Take away from the essay was, although he liked and welcame the low weight, he prefers having one stop more and get the shot at dawn or sunset.
The very few people who can afford and are willing to carry this kind of optics will most likely rent one and the decide if it suits their needs. I think it's hard to make a rig stable enough to test these things - and the usual test parameters might be useless if it has a) slow AF or b) issues with WR or c) can't take a bump.Roie Galitz took the new Nikon 500/5.6 PF with him to Kamtchatka to compare it with his 500/4. See also https://www.dpreview.com/articles/388997...-kamchatka
Take away from the essay was, although he liked and welcame the low weight, he prefers having one stop more and get the shot at dawn or sunset.