Which build should I choose?

[behaigo]

I have two potential 20th lvl builds I'm trying to decide between. In the long run, what will likely result in more damage overall:

6 attacks per round at 31/31/31/26/21/16 for 3d6 +21

or

1 attack per round at 51 for13d6 +30

[altpersona]

can we get a third option?

~70pts dmg / round @20 is 

[behaigo]

Yeah, I know they aren't all that good, but that's due to the limitations set by the GM.  My character is a Pathfinder-only Arcane Archer, and I've managed to get him a 17 BAB and CL, and the only spell I have worked into these is True Strike.  If there is a better build available I'm all ears. 

[altpersona]

my pathfinder-fu isnt top notch.

[behaigo]

Mine isn't either, which is probably why my damage is so low.  All that aside, which one should I choose between options I have presented?

[Maat Mons]

According to this thread, the average AC for CR 20 creatures listed in the 3.5 SRD is 36.44, and the maximum is 40. 

First we'll look at AC 36.  With +31/+31/+31/+26/+21/+16 (3d6+21), you've got an 80% to hit with each of the first 3, then 55%, 30%, and 5%, and your average damage is 31.5.  Your weighted average is (3*0.80+0.55+0.30+0.05)*31.5=103.95. 

Now we'll look at AC 40.  With +31/+31/+31/+26/+21/+16 (3d6+21), you've got an 60% to hit with each of the first 3, then 35%, 10%, and 5%, and your average damage is 31.5.  Your weighted average is (3*0.60+0.35+0.10+0.05)*31.5=72.45. 

With +51 (13d6+30), you've got a 95% chance to hit either AC 36 or AC 40, and your average damage on a successful hit is 75.5.  Your weighted average is 0.95*75.5=71.725. 

It looks like you'll typically want to go with more attacks. 

[behaigo]

Thanks a bunch, that was exactly what I was hoping for

[Halinn]

Assuming that you want to play an archer, I'll urge you to consider a Paladin archer rather than an Arcane Archer. The Litany of Righteousness spell, as well as the Pathfinder improved Smite Evil should combine to make short work of any target that is of the evil alignment, and if they aren't, you're still dealing a decent amount of damage just from strength bonus, whatever you're getting from the weapon, the Divine Bond class ability and the Deadly Aim feat.