I just recently did it as well, close to it. 1 toon was RGMercs/KA. SK,SHM,BRD,BST,BER x 2. The SHM was pretty solid overall, but there were some things I was attempting, that he couldn't keep up. I had to temper expectations, and then it was fine. I think 90+ I stopped having issues. 80's was rough.
I am a little confused on this one. Why the BST when pairing with Mages? I understand the desire for all CWTN, but I would swap the Mages for Berserkers and keep the BST, or 1 Berserker and a Rogue. Or Drop the BST and go 3 Mages? You already have slows/haste on two toons with ENC/SHM so what does the BST bring ADps wise to the group that really cannot make use of it in Casters.