Well, with this build your not going to cast anything that an 11th level sorc could not cast traditionally(You can still cast higher level spells by spell-draining them from other casters, though, and you can get scrolls of what you need in a pinch) so as a result stalwart battle sorc would actually be good here, so you can actually be more effective in melee when you want to be...remember, arcane gets some good buffs, but nowhere near cleric-level when it comes to melee. So if you want to hack things up(and with soul eater levels, you do) and are not really focusing on being a traditional, spell-focused caster(which your not focusing on here with only 11 levels in a caster class.) stalwart battle sorc becomes ideal.
I am beginning to like this build as a BBEG...I will have to stat him up eventually and perhaps use him against my new playgroup in the future.