Just pointing out this isn't necessarily a CPU problem, it could be an HDD problem. As you say, 3440x1440 at 60hz is a lot to calculate - roughly 297,216,000 pixels per second, or (using
math from the FRAPs forum) ~283.4 MB/s. If you're recording to platter drive, you're almost guaranteed to be saturating it. I see you have a pretty large SSD, but it's also far from ideal to record to the same drive you're playing your game from.
Your (cheap) options are to lower the record frame rate and/or resolution.
A more robust solution would cost more (such as multiple HDDs in RAID). Personally, I used Dxtory (not free, about $30 when I bought it) which has software striping, allowing me to record to multiple HDDs and then recombine them after the fact. (It has other nice features like recording to at a different resolution/fps than you're playing, recording separate audio streams, and even only recording a portion of your screen.) It's not perfect, but it has worked for me. (Never used OBS to compare against, though.)
Those stutters are driving me crazy just watching it! :P