In reaper:

+2 to all stats with a reaper bonus hat, so +1 all DCs.

+3 DC's in reaper with reaper tree

+4 casting stat through reaper trees

Net gain +6 DCs in reaper.

I recently discovered Embolden Spell does not apply to some things it should. Greater Shout and Burst of Glacial Wrath are two I know.