I believe the math is off. Master spellthief has all classes use the same CL that it calculates as the total of all arcane CL (other than ST) and ST levels. Here is my formula I was using to calculate it:
2(S+ASP)+KotW+ASP+ST
S is Sorcerer CL, ASP is Arcane spell power bonus (it adds to all arcane caster levels), KotW is actual levels of KotW (that is why S is multiplied because KotW is total Sorcerer caster level +1), and St is actual levels of Spell thief (they don't get an actual caster level until 4th class level)
I'm not sure how Illuman will factor into this yet I'll have to crack open that book and see.
You're right my math is off, but KotW also increases in CL due to UM, it's not just "Sorc +1". You're gaining spellcasting levels from UM in both classes, albeit unequally. So let me redo this.
Master Spellthief adds 1 to each CL, Krau Sigil adds +2 CL to every casting class, up to a limit of your character level (so apply this first, and you don't need Enhanced Power Sigils). Thus, we have:
Evoker = 18 levels + 2 from EPS + 1 from Master Spellthief + 4 from Arcane Spell Power = 25, and more if you took Spell Power from Archmage.
Knight of the Weave = 25 from Evoker + 8 levels + 1 from Master Spellthief + 4 from Arcane Spell Power = 38 (again, more if Spell Power from Archmage).
Thus, with (say) an Orb of Force ported over to KotW with Expanded Spell Knowledge and using Reserves of Strength, you would do 41d8 damage. Not bad... especially if you burned a 4th-level Evoker slot to Twin it for free. 2 4th-level slots for 82d8 damage, and you could spend 2 more to do Quicken another one. Since you have a ring of Wizardry IV (because you're ECL 20), you have a lot of 4th-level spell slots to burn...
If you took 5 levels of Archmage and took Spell Power for each one (I don't suggest you do this, but you could), you would have and Evoker CL of 30 and a KotW CL of 48.
If you took a greater bloodline, it gets even more fun because you get an extra +3 CL on Evoker and +6 CL on KotW... but you'd be 17th level at an experience level of 20. Unless you could take all 3 bloodline levels at 2nd level, and be 19th level (20th - 3000xp).
So... yeah.