Check the Magic accuracy and magic potency that's what i would do.
Wand & Shield - Thunder 80% ~~ Fire 20% ~~ Ice 0%
Magic accuracy - 229
Magic potency - 139
Staff - Thunder 0% ~~ Fire 10% ~~ Ice 0%
Magic accuracy - 134
Magic potency - 135
This is just from looking at it and adding it up with desktop calculator . I don't Know anything about the levels that Magic accuracy and magic potency cap at. Just from those two I'd go with wand/shield. Plus the fact that it has more of the element % that you like to use thunder 80% and fire 20%. again i don't know if the element % increase dmg or not but just trying to help lol. Not even sure if SE has caps on % either
In the End I'm guessing you'd get way more dmg out of your wand/shield setup plus im sure the shield would up your def
Edit: I may be completely wrong lmao who knows