Auto calling with rags heads-up

[Scott_Baio]

I was just in the finals of a sit-and-go and I won a large pot to the point where I outstacked my opponent 7 to 1.

Seat 3: HERO (6980)
Seat 4: the_other_guy (1020)
the_other_guy posts small blind (300)
HERO posts big blind (600)
** Dealing down cards **
Dealt to HERO [ <font color="red">2</font> [img]/images/graemlins/diamond.gif[/img], <font color="red">8</font> [img]/images/graemlins/diamond.gif[/img] ]
the_other_guy raises (720) to 1020
the_other_guy is all-In.

Should the hero call the remaining 420 here? There is 1620 already in the pot and hero will still have a 3 to 1 chip lead if he loses.

Now, I'm almost 100% sure the hero should call that. However here's the REAL question it brings up.

What's the highest amount you would call with any two cards in a similar situation? (talking in numbers of percentage of total chips vs percentage of your chips)