How Would BDD Effect an Application's Efficiency?

Question

I'm contemplating using BDD for a personal project of mine. However, it is a video game (a bio-sim game at that, coded in C# with XNA) and I'm not sure that the modularity BDD enforces would be beneficial in terms of run time.

Basically, the user needs to be able to speed up the simulation as fast as imaginably possible in order to traverse time more quickly; the faster the better. Thus, processing speed is critical, and I debate using BDD because modularity implies more function calls (I know, we're talking low level). However, I want to implement both an evolution and AI mechanic, and well... with so many interconnected engines, a suite of tests could easily save me a LOT of debugging.

Can anyone give me an informed opinion as to how appropriate BDD would be in this situation? Any recommended alternatives (besides finding more sane things to do with my time)?

Thanks