If you went
Spellthief 1//Fighter 1
Spellthief 2//Rogue 1
Spellthief 3//Rogue 2
Spellthief 4//Rogue 3
Spellthief 5//Rogue 4
Spellthief 6//Rogue 5
Spellthief 7//Rogue 6
Spellthief 8//Rogue 7
Spellthief 9//Rogue 8
Spellthief 10//Rogue 9
I'd get Sneak Attack 8d6 and the special abilities from both classes, correct?