I think the 2.4ghz i9 is the coolest "for a given workload".
But it doesn't matter either way which processor you get because any efficiency gain will be used to execute tasks faster, not cooler. But if you disable turbo or use Volta or voltage shift to keep fans under control, the 2.4ghz i9 will be fastest at a given fan speed.
I think the 5500m produces slightly more heat and/or power but both use similar power and both are equally problematic.
If you don't need GPU performance, get the 5300m and bump CPU to i9. If you do need GPU performance, get the 5600m or an egpu and bump the CPU to i9.
The eGPU option, if you can live with its quirks (quit some apps on disconnect) will be cheaper than the 5600m and the fastest CPU performance because dGPU only uses 0-5W leaving max power and thermal headroom for CPU. And 2.4ghz i9 can then run sustained at 3.9-4ghz. Very fast
The 2.4ghz i9 is the only processor I didn't consider, since it seemed like overkill.
Given the pricing scheme, if you want to upgrade to 1tb, it makes sense to just spec up the higher end model. That's how I ended up with i9 2.3ghz 32gb of ram and an 8gb 5500m. The higher end model starts with the 5500m 4g and it's only 100 usd to upgrade to 8gb. As I do some light video editing in bursts throughout the day I figured why not.
I also ordered a refurbished i7 2.6ghz model with the 5300m, but am sending it back since the battery is not great and I need more storage.
Does the 5300m draw less power in clamshell/with an external monitor plugged in? From what I could tell it does not, but if the 5500m is going to give me problems with thermals I can look at playing around with specing options some more.
I was going to possibly return the i9 2.3ghz with 5500m also because of heat issues discussed here, but if it's a wash with the i7 in most use cases maybe I won't.
If I can underpowered the i9 (2.3) to 27 watts (or use the dynamic power limiting referenced in the video above) and it will outperform the i7 while drawing the same power, then I may stick with the i9 model I have. But then there's the question of the graphics card... I don't need the 5500m but figured it might have a few minutes off my work every day.
Does the 2.4ghz i9 have better thermals than the 2.3ghz?
Im aiming for the coolest system that isn't crippled... like everyone here. The 5600m is beyond my price point... and would prefer to upgrade to 64gb of ram if I was spending more cash.