This helm (and much of the heartwood armor) seems almost an identical upgrade from the Tier 1 OoW items. The Sunrider's Hat has the following stats:
AC: +32
Str: +8, Sta: +7, Wis: +15
Disease: +7, Magic: +10, Poison: +8
HP: +115, Mana: +100
Damage Shield: +4
Regeneration: +4
So in other words, by upgrading to the heartwood from the sunrider, you have the following stat changes:
AC: +8
Str: +5, Sta: +5, Wis: +5
Disease: +5, Magic: +5, Poison: +5
HP: +20, Mana: +20
Attack: +20
Damage Shield: -4
Regeneration: -2
Mana Regeneration: +2
Effect: Plainsight