The EK PrC has 10 total levels, and 9 of those have "+1 caster level" for the spells. So, a Ftr 1/Wiz5/EK10, as written, would have 14 levels of spellcasting ability.
My modification was to remove 2 of the spellcasting levels from the EK, making the EK PrC grant only 7 total spellcasting levels, in exchange for d8 hit dice, and better will saves.
My player opted to keep the d6 hit dice, but take the better will saves, and getting a bonus feat, in exchange for 1 extra spellcasting level loss. So, his version of the EK has 8 total spellcaster levels.