I have played both Stamina and Magicka DK DPS builds and the tool tip difference is 10k+ damage with CP in mighty and all atts into stam versus Magicka setup.
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But, sometimes stam builds will get more damage from some ultimates whilst magica users will get more from others.
For instance, dragon Leap deals physical damage. A Stam user is likely to stack mighty whereas a magica one isn't. Therefore the stam user will get a bit more out of it.
Dawn breaker on ther oher hand, is magic damage. A magica user such as a sorc or even more specifically a templar/ nightblade, will put a lot of points into tharmatuge, which increases magic damage. So they will get more out of it then a Stam user.