It's difficult to compare the two because they are two entirely different things, it's like comparing apples and oranges. Cube2 isn't a game engine, it's a game that has level editing. GameGuru has a whole lot more to it than Cube2, and at first try won't be as fast and fluid as Cube2, this is because Cube2 is optimised for a specific task, whereas GameGuru is a game making engine, and you have to optimise your own levels. Even then to be honest, compared to other game engines, gameguru is a little slow and memory intensive, as there are various memory related issues, but i'm sure once those issues get ironed out it can be as fast if not faster than most mainstream engines.
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