You are probably correct and maybe/probably there is a difference about cpu cycles between the modes. However, I use the mode that gives me the best result for my application. That would be the most important in my opinion. At the end, settings of parameters and whatever else you have in your system determine what hardware you need. Reliability is another important and costly parameter. Yes, and the size of you expense account ;). So for me each application, each system is individual and must be tested. How about the cams; 720p, 1080p, … FPS, . Parameters that very much effect the need for hardware.
Your result is very interesting so please report back since it certainly will help others here in forum with same sort questions. We have a lot of questions about this and it might be an idea to include these results in some sort of guide lines.