It's as fast as C, since anything you can express in C can be expressed in BeefLang.
The real question is how fast an idiomatic expression of an identical complex program is in both language. Well, that might not even be the question- it may be more like "if presented with a problem that requires writing a program, what are the characteristics of the solution to that problem if the language chosen is X vs Y". Maybe?
Anyway, I don't think anyone has figured out how to properly compare programming languages yet in that way other than "try it and see if it works better for you than other things you've tried before".
