I thought quite much about how to express the issue in as few words as possible and at the same time to say the essence:

Which of the engines -- and I'm specially aiming at UDK -- offers in the best way, the possibility of making the simplest game with a corresponding low FPS?

This question I think reveals the best engine, besides the performance. Very tricky as some engines are not versatile and can't work with graphics below a threshold. I'm not implying anything about a certain engine; I just want to know more. Let's say we want to make a 2D game with no shaders, no nothing. Like a pacman or snake. Which of the engines is capable of making it and of those which can, which one yields the lowest FPS?