I'd just make Verwater/Verblizzard 150-200 potency but with a similar 5s cast time like on Veraero/Verthunder. Also, Enchanted Moulinet should be 250-300 potency.

...and maybe increase the potency of Enchanted Riposte to 250, Enchanted Zwerchau to 300, and Enchanted Redoublement to... 500.

I'd almost suggest an Ultima spell for an AoE finisher as well, but Iunno. :V