Tchoup

I have looked at OpenGL benchmarks, but as far as I know CM doesn't use the newest version, so it would be hard to get actual benchmarks.
GFXbench you can narrow the filter down to Desktop, Windows OpenGL, x86, and median score. This seems to be the most relevant result
https://gfxbench.com/result.jsp
https://www.guru3d.com/articles-pages/basemarkgpu-benchmark-review-with-20-gpus,3.html
etc.
I wonder if these cards perform any better or worse in terms of bogging down in heavy scenes, and loading bigger/more complex maps faster/smoother.

My question is back to the OP's focus on CM.  Will a difference between a 1660, 1660 Super, and 1660 Ti make a difference in CM's performance.  I buy a new laptop every year.  I have gone from a 1050, 1060, 1080, 1660, and now a 2080 Super.  All are mobile.  The only measurable difference I saw with CM was the move from a 1050 to a 1060.  The change in FPS was immeasurable.  Loading times seemed to improve along the way, but not execution.

Yes, you are correct. I am wrong.
The 1660 uses GDDR5, but they went with GDDR6 on the Super version (which I somehow missed in the OP, my mistake). This places the Super in between the 1660 and the 1660Ti, and I reckon makes it the best solution between the three if budget is a factor. If it isn't, the Ti is still the (slightly) better card. But the difference is so minor it probably wouldn't be noticed, and especially in a game like Combat Mission.  You could save a few bones and get similar performance with the Super.

I would opt for a "k" version of the i5's. CM sees an improvement in fps when you overclock the **** out of your cpu. Probably because it doesnt really use multicore as much as single cores

If you are never playing any game but CM, that is probably a very good balance between performance and price.  the i5 has better single core performance than more "powerful" i7/i9s.  I have a 1660 on my backup laptop and I see almost no fps difference between it and the 2080 on my main laptop for CM.  You can even skimp n the RAM as I don't think CM uses more than 4Gb.  A fast SSD is probably the one thing that might make a difference in loading times and the stuttering you might get when quickly changing views.

If you are certain that the rig is only going to be used for CM then your setup should do well enough. Couple of things to think about, what size screen will you be hooking up to the GPU now AND maybe in the future? The 1660 is no power house, I have the same in my solely for CM gaming PC and it’s served me well running at 2K resolution, and, although it’s capable of 4K, I rarely use it at that res, would probably look elsewhere if that was my preferred resolution. Having said that the in-game GUI is not optimised for 4K so there are other issues if you go down the 4K route. It might be worth your while looking at a second hand, older, but higher end GPU. Remember CM is based on an oldish engine so in terms of GPU - newest ain’t always necessarily best.
16GB of RAM is more than enough. SSD does help with loading times, and it’s generally helpful in the OS so, yes to that, but make sure you have a backup drive of some sort, and also somewhere to store all those lovely mods ...
If you’re happy to stick with Intel then the CPU will be fine. I don’t know about AMD CPU’s someone else will likely come along to advise about those as a possibility.
Really don’t need to go overboard speccing a rig just for CM, and as you rightly point out the CPU is really what determines how fast the game computes stuff.
Good luck