I don't think this is over training for me, everyones body responds different without a fact.
I work my legs out every 4 days. In between I use the stair mill, which gives me a great calf burn and not to mention a great tone on my thighs and legs all around.
With this combination I have gotten my legs more beef!!! Changing it up helps me a lot.
I do start with squats then jump over to the leg press. Sometimes I just squat and cut out the leg press and substitute something else in like, isolated leg xtensions.
The thing when I do squat and leg press at the same time my squat weight is not as heavy because I am more fatigued in my legs.
Without the leg press I can squat an easy 420. With the leg press I don't go pass 270.
Sometimes I just cut out the squat for the week and do the leg press and that is my baby where I can really rack the weight 1260lbs. I don't always lift heavy I always go for more intensity then weight, I gain more strength this way and able to put on more weight by going nice and slow, increasing my reps and sets and taking less time to rest in between.
Works for me.
Cheers.