If I set my game fixed to 120FPS, on my Alienware PC which is Intel i7 quad-core CPU, 8-threads, I get a blazing fast experience. It hits 120FPS easily on discrete GPU or integrated GPU. When I run the same game on both my dual-core PCs, one with Intel CPU 4 threads (Surface Pro 4) and the other with AMD CPU 2 threads (HP all-in-one), they both struggle and fluctuate between 20-50FPS! Nowhere near 120FPS!
Does a basic UE4 application, require a fast PC to run it? The thing is, in my debugs, the Tick() function on all the objects, gets the correct delta time of 8ms, which is 120FPS?
UE4 runs a bit heavy, but those machines are also very low-end
The Surface is using an integrated Intel GPU which don’t meet the minimum requirements to run UE4, and what also makes it more difficult is that they have a high resolution screen (bigger than 1080p) which pushes the game even harder, it wasn’t until recent years that games were running at 1080p much less higher than that.
I’ve got a project where I actually force the graphics to run lower on the Surface so that it can have smooth performance.
The AMD one might actually be worse
Thank you so much darthviper107! You have opened my eyes to this issue. I am convinced that my Surface and HP struggle to honour my fixed frame rate. It now makes sense that the Tick()'s receive the correct delta time as UE4 is trying to give me my framerate, but alas, the machines can’t keep up. My Surface Pro 4 actually has a Intel m3, which is the very low-end, and my HP has an AMD A9, again very low-end.
I ran the 2D side-scroller C++ template on my Alienware and timed it and it can hit a very steady 240FPS! Even my game with the camera set at 4K can pretty much manage 240FPS.
The Alienware has an i7-4770 (4 core/8 thread) CPU with 16GB RAM and an AMD RX 480 8GB GPU.
Good. Now when I come to release my game on the PC, I can spec the minimum requirements as something similar to this:
Intel i7 4th gen (8 thread) or AMD Ryzen 5 (12 thread) CPU with 8GB RAM
NVIDIA GTX 970 or AMD RX 470 GPU with 4GB VRAM
I will stick with 60FS on release and I’m guessing a PS4 and Xbox One will be ok.
The great thing is my Alienware is so quick at compiling the projects. 
Cheers!