I'm still with my Y580 (rarely turn on though, only when travelling) and still rocking Battlefield 4 at 720p medium.... XD
Though somehow Windows 8 decides to be a jerk to me, leaking memory all over when playing not at desktop resolution
Used to run fine, but this time it decides to give me headache... But, disassembly process and applied new thermal paste really worth the effort as it managed to keep the CPU and GPU well below 90'C (IIRC around 78 - 80'C) at Malaysian room temperature without any additional cooler...

Last time I run BF3 in US winter time (turn off heater, room well below 20'C) it runs 100'C
I ran The Sims 2 as well, 75'C for GPU but CPU is a little bit hot at 85 - 90'C...
So, whoever hasn't disassemble and replace the thermal paste yet you are recommended to do so... Once opened, you will be surprised at the quality of the paste Lenovo used... they really cut corners there... completely dried up for me... not to mention the thermal pads get thinned and didn't even touch the memories/vrms... after replaced, I've never touched 100'C even once on CPU and GPU...
at 720p, I don't think there's much problem... I played BF4 with medium settings on Y580...
I ayd replace my thermal paste long time ago (thermaltake one, forget which model tho), and while play game it wont exceed 90 degree C and will keep stay at 70-80 something....
And my Y480 is running fine with Win 8.1, just the USB 3.0 sometimes will haywire
After playing NFS Rivals....