A post recently from RPZip (can't remember which one it was) made some calculations regarding how big the nerf is, and it appears an effective drop from 11% (3.8 speed Thunder) to around 9.5% is what we can expect.
ofc, this is only Theorycraft, I don't believe that there has been any official comment on the extent of the Nerf.
Me, I'm staying with Thunder, I lose far too much top end damage and Stamina to change to either sword of axe, and the Stun (when it procs) is just too awesome to give up.