What settings I can change to improve performance and reduce stuttering of Magicka?

Solution 1:

Did you try again recently, with the latest update? They've been updating the game almost daily, and the last couple of updates (such as this one) have had an entry in the "Known Issues" section like:

• Game stutters slightly on some systems despite good performance (cause known, fix pending)

Today's update has an entry in the "Fixes" section that sounds like the same issue:

• Fixed high-end machine jitter.

So it may now be resolved.

Solution 2:

It seems to be a known issue, not fixed in the latest patch. The patch notes of Feb 24 state under known issues:

The game may appear to be stuttering even though framerate is good.