I find reading article a better barometer of real world performance than the stuff youtubers put out; I find that all to often these videos start out w/ a predetermined conclusion and then go out looking for facts to support it and this leads to picking only games that support it.
As for 144 hz Gaming ... depends on what are you looking for ? Playing all games at 144 fps ? ... playing most games > 60 fps ?
The 980 Ti is still a fine card for 1440p .... wasn't as attractive dollar foir dollar as twin 970s but broke 60 fps in all but 4 or so games in techpowerup's 16 game test suite. That being said, the 10xx series was an incredible step forward over 9xx and the 1080 Ti is about 75% faster than it's predecessor. OTOH, it's overclocking potential was far less than the 9xx series card @ 11.8% ... about 1/3 of the 980 Ti's 33%.
With a G-Sync monitor, you get the option of using ULMB instead of G-Sync from about 75 fps and up ... so I understand the 100 fps target. Current 165Hz 1440p monitors can do ULMB up to 120 Hz and 144 Hz can do 100 hz.
Out of the 22 games in TPus current 22 game test suite, these 8 don't make the 100 fps point w/ 1080 Ti, tho 2 come close:
Ghost Recon WL 60.6
Anno 2205 60.7
Dues Ex: MD 71.5
TW Warhammer 78.4
Watcg Dogs 2 78.6
Civil VI 81.2
Fallout 4 96.8
Dishonored 2 98.7
The other thing is that factory OCs aren't doing a smuch as they used to an nVidia has taken a page out of AMDs book and mot aggressively clocking cards in the box, leaving less OC headroom
But yes, the 1080 Ti will give you a substantial boost over the 980 Ti and, and I am saying this for the 1st time in many generations, cost and performance wise, moving up to the 1080 Ti will be faster than adding a 2nd last generation top tier card.