I have just started ToB and have Sarevok in my party (I couldn't resist). Is it worth dualing him to a mage do you think? My party at present consist of
Sarevok,
Mazzy,
Jaheira,
Valygar (but no Celstial fury AAAAAAAArgh!! Frustration!!!)
Imoen,
Myself (Necromancer)

Also I was thinking of swapping Imoen for Yoshimo. He does have much better theiving skills for a start and I could possibly dual him to a fighter for a bit of variety. Any help is welcome guys!

You have a party of 6, so the levels will go up slowly. There is no point dualing Sarevok because you find him at level 17, which means if you dual to a mage, you won't be able to use his fighting skills until level 18 mage, where you would be very near the end of the game anyway. He also won't be able to cast level 9 spells because he has 17 INT.

How do you expect to use Yoshimo. I assmue you've finished SoA so know what heppens??

If you removed Yoshi frpm your party BEFORE the end of SoA...I can tell you that...
SPOILER!
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...he dies in the end, you won't be able to use him, unless you cheat :D

Dual Sarevok to a Thief either now or at level 20. He's a grandmaster in Two-Handed swords, so make use of the Thief ability, Use Any Item and give him... are you ready for this? ... ...
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<font size="5", color="white">CARSOMYR! THE HOLY AVENGER!</font></center>

Imagine Sarevok, with Assassination combined with Carsomyr combined with his Deathbringer skill... ... ;)

*Guffaws*

I don't think it's worth dualing Sarevok.

cool idea.