[DD2] Bad Framerate(?)

I couldn't find any similar threads about bad framerate on DD2 and the search function on the official forums is garbage, so here we go.

I just picked up DD2 for the first time with the new patch and my performance has been less than expected considering my hardware. It's very unstable and occasionally it goes all the way down to sub 30fps in the extreme cases. Is this a common problem with the game or is something wrong?

System specs:

• i5 3470
• GTX 970
• 16GB RAM
• 1920x1080
• Windows 10
• 353.62

My friend with very similar hardware says his framerate is a fairly solid 60 at 3840x2160, so I'm not sure what's going on here.