when you can train a bodypart 3 times a week it means your workouts are not heavy enough
I train very heavy, the recovery time is the same for me. I don't train legs though, not weights anyway. Uphill running is about all my legs get as i have to stay around a certain weight.
...flame on...
I destroy chest, arms, shoulders, back, everything else...I always feel recovered in 48 hours.
As to what the optimal training frequency is, i have no idea, it probably depends on the individual.
Gymnasts train almost continually and they seem to do alright.