But in return, you'd get some cost reduction (and magicka DKs have expensive spells), and some magic resist, and DKs get bonus magic resist, so the more the merrier.
You might do ~6% less DPS, so you'd be fine.
PC NA CP 531+ Aedric Fury Sits Around Doing Nothing Sola Auroron Magicka Templar Lunaria Chimeri Magicka Dragonknight The Chosen of the Storm Stamina Sorcerer Ward-Scales Magicka Nightblade Sanctius Luxen Stamina Templar Nerwaye Auroron Magicka Sorcerer Warden Vyrkyl Stamina Dragonknight The Ninth Adventurer Stamina Nightblade Magna-Sola Magicka Templar The Celestial Lady Magicka Templar
Read their adventures! The Celestial Lady
Most would probably say ,yes, you would be gimped.
I have a 531 CP Berton mag DK and although they might not be the optimal choice for a mag DK I do just fine in PVE and PVP. I don't do any group dungeons or trials but can solo dungeons in Calgron no problem. Go vamp if you like PVP it seems to help.