My rig isn't the greatest, but an overclocked 650ti Boost should be able to run League at max settings at a stable 60 FPS. Without V-sync I've been getting around 120 fps constant until one of three things happen:
1- I die and my FPS hits 20 until I respawn.
2- I open shop and my FPS drops to 50~ until I close the shop.
3- There's more than 2 big animations on my screen. Things like Lissandras new hair, Morgana and any of her spells or Legendary/Ultimate skin animations causes my FPS to plummet very hard, to the point at which I have lower than 1 frame per second.
This is becoming a little annoying as I can run heavy games like Planetside 2 on my PC without any issues.
Hoping there's some form of issue with League and 650ti's