In my opinion the shims work great in reducing the heat transfer to the calipers and most especially the brake fluid. They have so far eliminated the soft brake pedal I used to get at the end of a session.
So though the piston side pad may run a little hotter the outer pad temp should not be affected (I only run shims on the piston side). I haven't noticed any difference in wear rates from before and after shims.
Were you running at the same track as before? Same session length?