on MOBs +/-10 levels he was able to control one stat while increasing another and see change the entire time up to 345 VIT

It would take the highest VIT gear and double melds on every applicable piece to hit 400 VIT... It is possible though
maybe we should....
What was your VIT and DEF, what MOB were you fighting and how much damage were you taking when you capped the VIT increase?

If you're really lucky and you could get 5 melds on each applicable piece... plus the right gear... you could get +300 Vitality... for like 560 Vitality on a Glad... I definitely don't see that happening though