Do you have anything else going on while gaming. Any multitasking such as youtube playing music videos or facebook open and minimized etc, or is this happening with just the game running?
You might be hitting the upper limit of the i5 CPU with the video card cranked up that high for 300 fps, if you lower the settings some you might find a better performance with possibly no noticable impact to gameplay and it will smooth over the stutter / lag.
Other causes for problems like this are if you are overclocking in any way, you can get tripped up timings. For example I went for maximum overclock of my old gaming system and it was stable with 12% overclock, but games would have a surge and stutter to them. I lowered my overclock to 10% and the games ran smooth. The surging and fraction of a second stutter was gone.
I have also seen systems with cheap RAM or mismatched RAM stutter games. Is this a single stick or a matched pair, as well as what make/model of memory is used?
I had a problem years ago with World of Warcraft having occasional framerate lag and stutters. A friend of mine asked what I was running for memory and I said 1GB which was plenty of memory at the time. And he said no... what brand. I said it was a single stick of PNY memory from Staples. He gave me a Corsair 1GB stick and said try this instead. I swapped out the single RAM stick and whalla... problem was resolved! When it comes to memory I no longer buy the cheap sticks. I gave him his stick back and bought a pair of Corsair XMS2 sticks, and upgraded to 2GB of RAM... this was back in 2009 when 2GB was plenty. Now days I feel that 4GB is bare minimum for gaming since the 64 bit OS wants about 2GB of it.
