So, you have Nvidia cards that support G-Sync, thats good. To me personally I don't see much of a difference in non competitive games with higher fps/hz. Others do see difference and I can't say if you will benefit from it. The IPS panel will have better viewing angles and you don't need to sit in the center with perfectg angle to it and IPS generally are known for good image quality and colors. If you would say you play a lot of games like Counter Strike or Overwatch where every frame/hz maybe relevant, then go for 144hz.
What resolution is it you want to buy? What display do you own currently?