This was actually a pretty big question, it seems!
So, is trained Evasion with equal Dexterity the best way to go, since it can far surpass even the largest DBs in causing the enemy to miss, right? Just train a huge Evasion with equal Dexterity and have Elven gear on the Evasion minion and that's your best bet to eliminate physical damage.
Also, with trained Dexterity equal to an opponent's Dexterity, you can eliminate Dexterity granted PTH by just having equal Dexterity, right? If an opponent doesn't have more Dexterity than you, then he doesn't get a Dexterity bonus to his PTH. I think that's what I remember reading, anyway.
So, DBs are the best if you already have huge Dexterity, since all of the opponent's Dexterity based PTH is +0, if they have equal Dexterity to you, so all that's left is to cancel out the +'s on the enemy weapon, and DBs can do that.
But, if you don't want huge DBs for NW or Encumberance reasons, then training Dexterity and Evasion would be the best way. BUT, if you want the most efficient use of your experience, so that you can save some for other skills, spells, etc., then you should just train Dexterity equal to your enemy's Dexterity to make his Dex-based-CTH 0% and get a huge pair of DBs.
Alternitively, you could train your Evasion level to 100, since that is the maximum Dex-based-CTH can get to and that amount of Evasion will cancel it out, leaving the DBs to cancel out all the +'s on the weapon of your opponent.
All that will force a properly trained Elven Longbow Archer to hit a maximum and minimum of once per round, or 80% of the time if you have all of the above training and equipment as well as an Amulet of Invisibility on the Evasion minion. I think BTH can never go below base, so since Elven Longbow has a base of 100%, it will always hit the enemy if Archery is at 1.0 effect, unless it is up against an Amulet of Invisibility. The only think that is confusing me now are the examples in the To-Hit wiki where it appears that the BTH actually CAN be lowered, but there is a minimum to how much it can be lowered. http://www.carnageblender.com/wiki/To%2dhit
I think it is lowered if you have less Dexterity than your opponent, right? Then, what is the minimum that you can take an enemy's Elven Longbow to? Is it always half of the weapon's BTH that it can be reduced to? I really thing I'm missing something key here.... I probably sound really confused with all that I've written. Could someone help sort all this out for me?