The feat in question is Avenging Resolution and it reads:
"When you attack a target of your otah of enmity with a weapon attack, treat all rolls of a 1 or a 2 on the damage dice as though the result were a 3 on the die."
Here's a level 4 version of a sample Elven Avenger with a Falchion instead of a spiked chain (Oath doesn't apply against non-adjacent targets, so reach isn't very useful for Avengers).
This particular build would have +11 vs AC, roll twice, 2d4(min 3 per d4)+8 damage.
DPR with Overwhelming Strike against an average level 4 enemy would be:
[sblock=DPR 15.11]Enemy: AC 17
+11 vs AC(+5 Wis, +2 Level + 3 Proficiency + 1 Enh)
Miss: .063
Hit: .839 x 6.5(2d4, min 3) + 5(Wis) + 2(Valenar feat) + 1(Enh) = 12.17
Crit: .098 x 6.5(high crit 2d4, min 3) + 4(+1 weapon 1d6, min 3) + 3.5(Executioner bracers 1d6) + 16(maximized hit) = 2.94
Total DPR: 15.11[/sblock]
[sblock=Sample Avenger]====== Created Using Wizards of the Coast D&D Character Builder ======
Falco Venger, level 4
Elf, Avenger
Avenger's Censure: Censure of Retribution
FINAL ABILITY SCORES
Str 10, Con 10, Dex 13, Int 15, Wis 21, Cha 8.
STARTING ABILITY SCORES
Str 10, Con 10, Dex 11, Int 14, Wis 18, Cha 8.
AC: 18 Fort: 14 Reflex: 16 Will: 19
HP: 42 Surges: 7 Surge Value: 10
TRAINED SKILLS
Religion +10, Stealth +9, Acrobatics +9, Perception +15
UNTRAINED SKILLS
Arcana +4, Bluff +1, Diplomacy +1, Dungeoneering +7, Endurance +2, Heal +7, History +4, Insight +7, Intimidate +1, Nature +9, Streetwise +1, Thievery +3, Athletics +2
FEATS
Level 1: Valenar Weapon Training
Level 2: Avenging Resolution
Level 4: Power of Skill
POWERS
Avenger at-will 1: Overwhelming Strike
Avenger at-will 1: Radiant Vengeance
Avenger encounter 1: Avenging Echo
Avenger daily 1: Aspect of Might
Avenger utility 2: Avenger's Resolve
Avenger encounter 3: Sparking Wounds
ITEMS
Falchion of Oaths Fulfilled +1, Stoneskin Cloth Armor (Basic Clothing) +1, Amulet of Life +1, Executioner's Bracers (heroic tier)
====== Copy to Clipboard and Press the Import Button on the Summary Tab ======[/sblock]