(TOB SPOILERS)
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While both spells are based on the caster's WIS, Wish produces random results. With Wish, you're given a choice between 5-7 options out of the 20ish that Wish can offer. However, having a high WIS (18 or so) can increase your chances of getting a better set of options.
Dan Simpson's SOA and TOB FAQ at gamefaqs.com (
http://www.gamefaqs.com/computer/dos...me/919881.html) describes the different options each spell gives. But really, if you gulp a potion of Wisdom and read a Wish scroll, you're bound to get the option you want.