For Fred's questions:
1. Always the same number of monitors connected, one control and one stage, and reconnecting them as needed on the desktop. On the original laptop, there's the laptop's built-in screen for control and an external monitor for stage.
2. Except for the one sentence about task manager and resource monitor in the original post, all the percentages and usage stats so far are from Isadora's load meter.
Going with GPU-Z, the results are interesting in different ways. When on the RTX, GPU-Z GPU Load roughly matches Isadora load, at around 30% on average with my test shows. When on Intel, GPU-Z GPU load is about 10x the Isadora load, averaging 15% and 1.5% respectively.
3. I'll try that test hopefully towards the end of this week.
4. Real world performance difference. The original reason was because of an actual problem - my TD was doing all the things we'd assumed worked when running a show and it was stuttering to a freeze. Since these laptops I'd spec'd should handle shows even better than the desktops from 6 years ago, that was weird. Then discovering that forcing Isadora to the integrated graphics - against the advice of one of the Isadora troubleshooting articles - made it run essentially perfectly, made me think that more experienced users might have some insight as to what we were doing wrong.
At this point knowing that the numbers we're seeing are normal and finding out the best way to set up our hardware for the future is the goal.
Now that DusX has confirmed my numbers I'm feeling more confident about what I'm seeing. And once I'm able to test both your theories by throwing a lot of layers and effects at the cards I'll have a good idea of which numbers are telling the truth.