Compare them during the first or last few minutes of legal hunting time. The exit pupil increases from 4.4 to 5.6 mm. All other things being equal, the larger objective scope will allow 25% higher magnification at equivalent brightness.
depends on how young and how good your eyes are. With perfect vision you may detect a small increase in light gathering at 9x but my old eyes sure dont see the differnce. given the choise id take the extra 100 bucks that 50mm ojective costs and buy a 3x9 with better glass. example would be id take a vx2 luepold 3x9x40 anyday over a vx1 3x9x50. Or a nikon monarch 3x9x40 over a buckmaster 3x9x50.