Karadjgne :
You might get another 1-1/2 yrs on a750/750ti, but after that, it'll pretty much be "gaming obsolete".
If you pay more you get more life out of the GPU, If you want 60+ fps then expect to replace the GPU every two years and your CPU every 3 years. What I consider Obsolete is "fails to be playable even in low" that would be something like a 8800 GT. A 750TI and even a 650 TI will still have enough power to hit Low settings in 3 years. Now for him wanting 60+ FPS a 750 TI wouldn't do that at launch much less now, lets be reasonable here.
$120-$175 - Expect 2-3 Low to Medium Settings "Expect lower fps and Spikes"
$180-$275- Expect 3-4 Years Medium or Mixed High "Expect less Spikes and Higher fps"
$275+ Expect 4-5 Years Medium and better Expect "More Stable fps but wont hold 60+ all the time"
I don’t recommend upgrading your graphics card unless the replacement card is at least three tiers higher "From Toms Hardware"
Any one that still owns one of these can contest that they still work beyond your expect 3 year life. GTX 580, GTX 670, HD 5970, 7870 LE (XT), 7950, 280, 285 notice where these fall in Launch price range and how old they are.
Bad PC Ports like Far Cry 3,4, Arkham Knight, Witcher 3 and so on need Higher end Hardware to push through the bad code. GTA V which initially was a bad Port is now optimized to a point that it will run with tweaking on CPU/GPU combos that are far below the minimum specs. Old MMO's that have API's based on DX 9 like WoW and GW2 are pretty CPU dependent, although they may try to update they still use the CPU more than they should so GPU's matter far less. Most of these games you wont notice a difference between a $175 GPU and a $500 GPU.
How cards compare look here, How long something lasts depends on your expectations not everyone cares about Ultra 60+ fps or even 60+ fps.
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html