But I mean, will 70-75 FPS be a meaningful increase over 60 or do I really need to hit 80-90-100 to make use of that higher refresh rate?
There are 2 things you can do.
1) You run your game with G-Sync. That means that inter-frame gaps need to be between 33ms (=30 fps) and 7ms (=144fps). Anything between those two will be pretty smooth with G-Sync.
Note, people bought 120Hz monitors before G-Sync. Because a 120fps game on a 120Hz screen is smoother than a 60fps game on a 60Hz screen. If you can run your game at 70-75fps on a G-Sync monitor, it will feel (slightly) smoother than 60fps @ 60Hz.
2) If you can run your game at 85+ fps, then you can choose to use ULMB (Ultra Low Motion Blur). ULMB works at 85Hz or 100Hz. With ULMB the motion blur in fast games get significantly reduced. But if fps drops under 85, you will notice a little stuttering.
Also - I'm using 1080p HDTVs right now, not sure how that factors into the AHVA-IPS-TN thing-
I bought a XB270HU for G-Sync and maybe ULMB. And because I wanted a 8-bit panel (less color banding). I didn't care much for 1440p. And I didn't care much for better colors and view-angles.
Today I sent back my XB270HU. Because of backlight bleeding. I hope my replacement arrives on Friday. I just put back my 3-year old Asus 27" TN 1080p monitor. Holy moly ! What a difference. I can't live with 1080p anymore. The screen is all pixelated. 1080p is not good anymore. Also, the colors are so more worse. Before I had the XB270HU, I just didn't know better. But now that I've had the XB270HU for 3 days, I know what a good screen looks like. I'm sure your HDTV is nice as a tv. But as a computer monitor, I don't think it can be even close to a monitor like XB270HU.
When I ordered my XB270HU, I was wondering if I should buy an Acer XB270HA. That's another monitor. That one is 1080p, TN, but still 8-bit and with G-Sync and 144Hz and ULMB. But today I know for sure, the XB270HU (with IPS screen and 1440p) was the right choice.
You just don't know the difference until you've seen it with your own eyes. I was a skeptic, but now I am a believer.
Too bad I'll probably buy a new videocard to push 1440p, when new games are released. Like GTAV and The Witcher 3. That's another 600 euros for a gtx980 to replace my gtx680. And 110 euros for a waterblock. My current gtx680 is good enough for G-Sync with most games. But I'm not sure about newer games.