All the builds herein were created as Point-Buy Characters (DMG p. 169) utilizing 28 points.
SRD + OA only Sohei
Starting ability scores: STR 16, DEX 10, CON 12, INT 14, WIS 14, CHA 8
(1) Human Paragon 1
(2-6) Sohei 1-5
(7) Psychic Warrior 1
(8-16) Slayer 1-9
(17-20) Sohei 6-9
Important skills: Must pick Knowledge: Dungeoneering as class skill @ 1st level and put 4 ranks into it
(1) Improved Initiative
(1 - Human Bonus) Track
(3) Quick Draw
(6) Combat Expertise
(7 - Psychic Warrior Bonus) Improved Trip
(9) Power Attack
(12) Psionic Weapon
(15) Deep Impact
(18) Greater Psionic Weapon
This combination meets all the high points of the Sohei up to Mettle and also nets psionics as a Psychic Warrior of Lvl 9.
If you don't need Mettle, you can replace the last 4 levels with 1 more level of Slayer and 3 more levels of Psychic Warrior.
Outside of SRD+OA, a cheap Least Crystal of Weapon Return(MIC) could replace the Quick Draw feat. Illumian (Aeshkrau) can make you less WIS-dependent in favour of more STR, and you may consider the Apprentice feat in place of Quick Draw to get Knowledge: Dungeoneering as a class skill skipping Human Paragon.
Starting ability scores: STR 14, DEX 10, CON 12, INT 13, WIS 16, CHA 9
Cloistered Cleric 1
Ordained Champion 5
Knight of the Raven 9
(1) Combat Expertise
(1 - Human Bonus) Tireless
(3) Improved Trip
(6) Power Attack
(6 - Cloistered Cleric domain replacement) Knowledge Devotion
(6 - Cloistered Cleric domain replacement) Travel Devotion
(7 - Bonus Feat in lieu of Diehard again) Extend Spell
(9) Persistent Spell
(12) Divine Metamagic: Persistent Spell
(15) Practiced Spellcaster (Cleric)
(18) Raging Luck
This one allows you to cast spells as a 12th level Cleric (with a CL of 16), as a Sohei of 5th level, meets the high point of Stun Immunity, and also to cheese around with DMM Persist.
Partial Gestalt Sohei