On line games such as LoL are prone to lag due to the nature of your internet connection. Ping, the server the game is running on, and the amoung of action at a given moment. LoL and WOW are both a bit notorious from what I've read on various forums.
V-sync will hold your fps at the refresh rate of your monitor as long as the system can produce a consistant frame rate well over the monitors refresh rate when V-sync is not in use, but it is not an fps lock.
If your system drops significantly below the refresh rate without V-sync fps will drop with V-sync on as well, perhaps more, as V-sync is somewhat system intensive (sucks up some VRAM I believe). It could help smooth out the drops that come from brief system lag by reducing resource use a bit on whatever it's not using itself, though (cpu ? ). So in your case of getting up to 80fps it could help keep the lows a bit higher.
Triple Buffering is for Open GL, so is not supposed to be beneficial with D3D games, but some swear it works anyway. It was supposed to help those who suffered with mouse lag when using V-sync.
So, it comes down to the game as to whether you use V-sysnc, or Triple Buffering, or not. I tend to only use V-sync when there is tearing due to too high fps, or if I know my machine is going to run the game at, say 50+ fps over my monitors 120Hz refresh rate. I don't often notice lag unless I've tried settings that are too high for my machine, but not using an fps meter keeps me in a blissful state of ignorance, which may help with not noticing lag too .
03:21 AM by