If you look at the specs you will find that it has a turbo mode of up to 4.0 Ghz. https://ark.intel.com/products/122589/Intel-Core-i7-8550U-Processor-8M-Cache-up-to-4_00-GHz
The 1.8 Ghz speed can be considered a "guaranteed" all core speed it should be able to run at indefinitely at the standard 15w TDP (as long as the cooling system is in good shape). 4 Ghz is likely to be a single core turbo speed that can be run for a short period. For example, when you open a large application, there is a period of high CPU activity as the program loads and initialises. This is a situation where, battery power permitting, you might see the processor turbo up to near full speed before slowing down once the CPU use settles down again.
With these laptop CPU's it's not obvious what the actual performance will be because it depends on the laptops cooling ability, and the way it's been set up by the manufacturer. Simply, they are thermally limited. The manufacturers can set short and long term TDP limits, and have the option to increase or decrease the TDP limit to modify performance. Typically larger laptops which can incorporate better cooling, should be able to run faster than an ultra small laptop, all other things being equal (even using the same processor). Some more comments on this processor here - https://www.notebookcheck.net/Intel-Core-i7-8550U-SoC-Benchmarks-and-Specs.242108.0.html
They sum it up as "In our usual benchmarks, the average i7-8550U is as fast as the 35 Watt rated Core i5-7440HQ" - so yes it should be able to run GTA V acceptably. That CPU matches or beats the much older i5-3470.
Also of major importance for gaming on a laptop is the GPU. The one you linked to uses a Geforce MX150 GPU, which is a mobile equivalent of a GT1030. It's quite efficient but really should be considered entry level as far as gaming GPU's go. It should be able to play GTA V on medium or lower detail settings. https://www.notebookcheck.net/NVIDIA-GeForce-MX150-Benchmark-and-Specs-of-the-GT-1030-for-Laptops.223530.0.html
Edited by jonuk76, 24 January 2018 - 03:02 PM.