That depends on your IHS.
The default - non-vario - coldplate curvature is based on the average curvature of commercial CPU IHS. The more yours deviates from the average, the more advantage you get.
My 8086k is lapped, so i get like 6-7c for some of the cores, this is about the maximum you can expect.
Well, I'm running a lapped J-batch 5960X at 4.6Ghz, so it does run hot and it's only cooled by a Supremacy MX, so I was definitely angling for a Cuplex Cryos (with Vision) of some kind. Maybe the PVD one.
I was just worried about diminishing returns - I'd heard only 2ºC was to be expected with the Vario, but if I could shave 7ºC then the extra fancy Vario might be worth it...