Hi,
Try 720p @30fps using ultrafast preset and 2000 bitrate with CBR see if this stops any "Number of lagged frames due to rendering lag/stalls: 291 (7.2%)" which is showing up in the log. Also stick to x264 software as its better with lowers bitrates. If than Nvenc.
If you are finding the i7 4820 can't handle 720p drop is down to a lower res as this will free up some CPU. if that fails then you can look at Nvenc as the final option as this uses a dedicated gpu encoder freeing up the CPU but at low bitrates the quality can suffer and is best used for recordings.