Hello again,
dantheman0809 is absolutely right with CSGO (due to it being on the Source Engine which has been modified by Valve for years - you'll get really high frame rates with that) but for the other games you've listed you'll not get above 60fps.
In answer to your question, will you miss out on 144Hz - unless you get another graphics card in SLI (and even then it's debatable) you won't be reaching 144Hz with Ultra Settings.
http://www.bit-tech.net/hardware/graphics/2014/09/19/nvidia-geforce-gtx-970-review/1
As I said above, it sounds like I'm scoffing at your card but please don't think I am. If I had the money, I'd upgrade my 670 to a 970 in a heart beat. But as the reviews show, 1080p @60 - 80fps Ultra Details, or 1440p at ~40 - 60fps @Ultra Details for most of the modern games.
I'm curious, do you know what sort of problems you will run into if you run a game at lower fps than the refresh rate of the monitor? I have heard from some people that it is not very noticeable but i'm not entirely sure and I would like to get some insight from mulitple sources
So in my opinion, get rid of the idea of a 144Hz monitor. Don't worry about it, as you're not going to see 144fps. The G-sync; that's another question - it synchronises your refresh rate of your monitor with your GPU. But you pay a premium for this tech. I wouldn't bother.
Hope that helps