I tried League of Legends and DOTA 2 a bit. They are both playable. LoL is less demanding than DOTA. LoL works in full resolution. I have the i5/8Gb/256.
Now I play Elder Scrolls Online. It runs okay at 1280x720 with textures and subsampling at High, everything else on Off.
You have to install the latest Intel driver and set it to Maximum Performance. Also you can try the Intel XTU. I was able to undervolt to a very stable -59mV for CPU and Cache and - 79mV for Graphics. YMMV. Also the Windows power plan should be set to Performance, this sets the Graphics from 600 MHz to 1000 MHz.
Whatever game you try you have to unset Antialising and Shadow as Intel does not support this.
Also, as you can see, an external cooler blowing air on the upper right back of the Surface helps as the SP3 is power throttling. You can use the Intel XTU to monitor this. Note that it is not Thermal throttling but Power throttling. Likely a sensor in the SP3 is cutting the power above a certain temperature and that is why an external fan helps.
Don't forget that Intel produced a special edition of their CPUs for the Surface. The silicon die is the same but the casing is different, that's why it is different.
Hope this helps.