As I pointed out, and as confirmed by Matt King's explanation, a shorter lens to easel distance does not mean a brighter image for the same size print from the same size negative. The determining factor for brightness is the degree of magnification, not distance per se. This is a common misunderstanding.
As for the maximum aperture, yes, f4 will indeed provide a brighter image than f5.6. But the point I was making, was that Soviet lenses are quite well known for requiring a fair bit of stopping down before achieving good performance. Depending on how critical you are about things like corner-to-corner sharpness and minimal vignetting, you may find that you have to stop down that FSU lens to f8 in order to get similar performance to the EL-Nikkor at f5.6, thereby mitigating any possible advantage regarding brightness.