M4700 hotter than M4800?

I'm looking at buying a used M4700 or M4800, and I noticed in the notebookcheck reviews that the M4700 gets significantly hotter than the M4800:

https://www.notebookcheck.net/Review-Dell-Precision-M4700-Mobile-Workstation.81505.0.html
https://www.notebookcheck.net/Review-Dell-Precision-M4800-Notebook.104416.0.html

The underside of M4700 gets up to 55 degrees, while the M4800 stays below 40. They have basically the same case and similar parts, same TDP for CPU and GPU. Does anybody know why this happens? What exactly changed in the M4800 that improved cooling so much?

 

Seems they were able to get 130W out of the 4700 at full load, and only about 107W from the 4800. The 4700 has dedicated graphics, no Optimus and averages more power consumtion. The 4800 has Optimus capability and can run more effeciently.

They also note the fan noise of the 4800 is "vehement" so it's possible they put in higher rated CFM fans in the 4800?

 

M4700 also has Optimus, unless you have the IPS display panel (which they yanked from sale pretty early on).

 

Maybe it was an optional feature depending on region? The 4700 NBC received could have been an early model, they do denote an IPS screen.

"The processor graphics unit Intel GMA HD 4000 is deactivated in this system, and cannot be used with the automatic switching provided by NVIDIA Optimus."

 

In both models the Intel GMA is disabled due to the screens being used. The difference in cooling is not related to Optimus. The fans may be more powerful on the M4800.

There are also 2 versions of the M4700 CPU heatsink. One has one heat-pipe (NNGFH), the other has two heat-pipes (80D8V). Maybe the laptop in the review had the first version.