I'd rather take the equivalent marathon time (whatever that is, I could care less) over a 4:00 mile. Knowing I've put in a 4:00 mile-type performance for a marathon would mean more to me than running a 4:00 mile, simply because I prefer long distance racing over middle distance racing, just as I would rather run a 4:00 mile than a 4 minute mile equivalent at the 100 or 200 meters, as sprinting is not at all what I'm into.
That being said, the notion that whatever the marathon wr was at the time the 4:00 mile was first achieved would be the equivalent is bogus. Hardly anyone was running the marathon back then, and with no magical time goal, but many were racing the mile, and guys were ferociously gunning for the sub 4.