000) It's usually quicker and cheaper to just throw in a box extending ring.
00) It's cheaper to just stay with basic 4s boxes -- deep -- and to use 3/0 rings -- 3/4" deep for all exit signs in a soft lid. (Occasionally 1" deep)
0) The spider ring -- always provided in an exit sign kit -- squeezes the tile between the 3/0 ring and itself -- which stops it from floating away during trim out.
1) It's much quicker to drill out the penetration with a hole-saw.
2) Space headaches are gone.
3) The geometry of support gets simple. Everything always lines up perfectly.
4) CADDY makes bar supports that mate perfectly with this scheme -- look at their product literature.