

Average damage over the first 2 rounds of combat is comparable to your vanilla two-handed weapon Fighter at this level. With Psionic Weapon(sp?) feat, Sneak Attack, and the psychic weapon thingy (bonus d8), he is doing d6+2d6+d6+d8+2 during the Surprise round, and d6+d8+d6+2 on following rounds (if he has the Flank and can spare the MEA to recharge his weapon, which can usually be arranged). I would say that I have seen a low level Rogue1/Soulknife4 in play that is doing very well. SoulknifeX/FighterX) the special weapon is essentially worthless once you hit mid levels.

The reason to not multiclass the Soulknife is that its primary ability, the special weapon, is likely to be approximately as good or better than the best regular magic weapon in the party if you stick to straightclassing.
