The nVidia tax is what tanked G-Sync. The price premium to get a half decent 4k display with G-Sync is absurd. nVidia has to understand that if you force people to pay for the GPU with one kidney, you can't try and force them to buy an overpriced G-Sync monitor with the second kidney as dialysis is kind of expensive and you're going to be fresh out of kidneys.
That G-Sync tax as you put it is based upon the mistaken assumption that G-Sync and Freesync are the same thing. In once sense they are in that as named, both provide adaptive sync. However, the G-Sync package is not the same as the Freesync package.
-Freesync provided adaptive sync technology which kicks in at about 40fps. While it continues to 'sync" above 60 fps, the observable impact diminishes the further you get past 60 fps.
-Gsync provided adaptive sync technology which kicks in at about 30fps. While it continues to "sync" above 60 fps, the observable impact diminishes the further you get past 60 fps. However, the "G-sync Monitor Package" also provides a hardware module which probides Motion Blue Reduction technology (ULMB). In any game where you can maintain 70 fps or so, with the sync effect dimishing the higher you card can mange, ULMB provides an experience that most gamers view as superior to adative sync in any form. AMD has no corresponding technology. Although some monitor manufacturers did provide some for of MBR technology with the early Freesync models, the number of such offerings has diminished.
That's due to the conflict in how Freesysnc is marketed. It's supposed to be the less expensive alternative to freesysnc, .... but when it's equipped to compete head to head with G-Sync and ULMB by providing a hardware module for MBR, the "G-Sync tax" disappears. If you want to play at 1440p, especially at high refresh rates, then nvidia can deliver a lot more fps as well as the ability to virtually eliminate motion blur. As such, I'd recommend:
60 fps @ 1080p in Witcher 3 - 144 Hz TN Monitor w/ 1060 3GB w/ MBR capable monitor
40 fps @ 1440p in Witcher 3 - 144 Hz TN Monitor w/ 1060 6GB & G-Sync or w/ Fury & Freesync
100 fps @ 1440p in Witcher 3 - 165 Hz IPS Monitor (AUOptonics Panel) w/ 1080 Ti & G-Sync
75 fps @ 2160p in Witcher 3 - 144 Hz IPS Monitor (AUOptonics Panel) w/ 2080 *
* Would recommend the Ti (even 2) but won't until the 10xx series stck is sold out and tariff disappears so that price gets back to normal levels. However, I don't see 4k as a real option for all but the "money now object" crowd for at least one more generation.