With 10.87, using H265, 720 export of 151211 had no failures at manual bitrates of 25000 or this 40000... 
No stutter seen with the H264 encoder.
Same with 150555 - no stutter with H264. Using H265, High Quality export was about 418Kb/s but manual 40000 was 26.1Mb/s.
720 export of that file at 40000 with H265 took 55 seconds. Using H264, six seconds. Frame rate variable 30.
So unable to replicate your findings at this time.