Quick question about crits.

What exactly is the difference between 475 and 490 defense in terms of crit percentages?

I understand that 275 is to be crit immune to level 70 mobs, and 490 is needed against level 73 bosses. But, what extra percent crit chance does a level 73 boss have against you that makes you need that extra 5 defense per level?

In other words, if I had 475 defense and fought a level 73 boss, what % chance would he have to crit me?

it's .04% to be crit for every point of defense you are blow the cap for that mob level. For example with 475 defense against a level 73 mob you'd have a .6% chance to be crit.

That is exactly what I needed to know, thanks. =)