You are not getting the full picture here. Clock speed isn't the only thing that affects your computers speed. Ram quantity, ram speed, cpu clock speed, cpu IPC, architecture, and so on and so forth contribute to the overall performance.
0.1Ghz will not be noticable, not when the architecture is the same, the IPC is the same, the ram is the same. On a 4K video export, what diference would it make? Instead of taking 1 minute and 52 seconds to render, it would take 1 minute and 50 seconds to render. Is that 2 seconds a 200$ worth upgrade?
Also, the more clock speed you have, the more heat you have. The more heat you have, the more the fans will go up. If they can't go higher, the cpu will automaticaly clock down until temperatures are within reasonable values. In a desktop, this rarely happens (this "phenomenon" is known as throttling), but on a laptop, specialy a thin one like the Mac, this happens a lot.
That's why the other user told you that the 2.7Ghz Haswell cpu wasn't worth compared to the 2.5 Ghz one, because due to throttling both would go down and end up performing the same.
Skylakes produce less heat and thus throttle less, but still a 0.1 Ghz upgrade is not worth. Consider investing your money in more RAM or a dGPU if you are not alreaddy thinking on that.
Personaly I indend to code on my laptop. Use virtual machines. And game ocasionaly. So whatever succeeds the current 15'' with 512 gb of storage, 16 of ram, and a dGPU, I will buy. If I have spare money, I will put it on RAM, not cpu.