I concur with the idea of GulliBell, the question has academic merit mostly, because:
My impression, its hard to enter Vortex ring you have to be looking for it, and even still before it happens, you get so much vibrations and uneasy feeling that any normal pilot would wake up look at the instruments and make the proper correction.
if you know where the wind come from, keep your airspeed in the green, don't go crazy on your rate of descent and add bunch of power to fix it. it does not matter 300 or 500ft per minute, you are nowhere close.