draw bar question

In a word: LEVERAGE.

With the shank pinned in the 1200lb position, it is closer to the truck and reduces the amount of leverage the spring bars have on the truck's receiver.

You're right, at 640lbs it does not make any difference which hole you use. The only reason to use the longer hole is if the tailgate hits the jack on the trailer, and being that much farther away will help.

All depends on how far you want your shank to stick out, not going over the rating. I one upped and drilled a hole even closer. Helped when towing with the Liberty. Works now with the Ram, except I can't open the tailgate.

Haven't seen one of those in a while but IIRC the 1200 lb hole puts more of the shank in the receiver which results in the higher capacity