Quote from Oberynn;1270395:
Even if you reach a breakeven point, S is still better. First of all, barely reaching a break-even just makes things equal and there is a large difference between equal and better or noticeably better.
Secondly, magic is not a DPS skillset and it aggro grabs everything, so it's better suited to stronger normals than overkill crits.
Also, magic has 100% balance. The argument of "critical portions ignore the balance stat" has less weight to it than it does with other skillsets.
Firebolt would be a candidate if the Spirit Fire Wand didn't render upgraded variants entirely obsolete.
The exception is Meteor Strike; where normal hits nearly always suck compared to critical hits.
You could also make an exception for Thunder, as the barrage all but ensures you'll deal some critical hits. Naturally one has to question why you're trying to maximize the effectiveness of said spell. On that note, why is OP making a wand for Fireball use?