I have been using my own version of a giant deciever for years on the spring herring run. Tied standard style, with the longest deer tail and saddles possible. I've experimented with different hook sizes and found smaller hooks cast better but don't sink well and have lower hooking success. Larger hooks cast like cannon balls and sink much quicker but have good hooking success.
I've often felt the need for even bigger flies, especially back when full grown bunker were the going fare. I never have set upon a useful giant fly bigger than the one described above. At least not one I can cast with the 9 weight Sage.