I'm in nearly all 63's. Don't have my stats off the top of my head, but generally speaking (while stimmed) I am around
30.5% def (low 500s rating)
65% shield (with rocks)
60.5% absorb (high 500s rating)
27.5 ish health
I've main tanked everything in the game except for Kephess on NM EC (only because he haven't downed him yet).
I've run numerous combat logs against the Guardians/Vanguards in my guild. Generally speaking, the difference in damage in is nominal - maybe 15 DPS difference on 800 something or so. The main difference is the fact that I generally average about 100 heals per sec give or take. This always makes me come out on top if you subtract that from the DPS in. If you were to trade out the high defensive stat mod/enhance for the high endurance, sure your HPS may jump up a bit, but in reality, i'd rather avoid an extra big hit than have 6 more HPS over the course of the fight.
I don't like the idea of maxing out any of the stats to be honest - I always liked the idea of a balance of everything. By the time you are in full 63 mods, you are so far into the DR area, that it's really up to you and what you feel to determine which way you want to go. The last time I did the math and analyzed the fight, I noted that defense was worth more to me than abs was at this point. This was different from vanguards/guards because of the flat dmg reduction they got from heavy armor. Basically, an avoid meant WAY more to a shadow than it did to any other tank. If we get hit past shield, it hurts pretty bad.