if it says it requires a higher stall, it is because the powerband of the motor has been shifted to a higher rpm band ususally due to the camshaft. so if you use a factory stall converter, it will be a slug off of the line until it gets wound up into the rpm's where it starts making power. you won't be able to lanuch very hard off the line if you try to race it.

if you have too big of a stall converter on a street driven car it will not have very good street manners. but that would be like a 3,500 rpm converter or higher.

2003 ford lightning
1959 chevy 36