John:
IMHO, the 'common sense' aproach should be used. Back in time..8' channels were heavy, made of real metal, and had heavier mag ballasts, so...additional support was required.
What do the plans/spec indicate; if anything. Also, I (IMHO) would check out the grid. Some 'new' grid is pretty flimsy, and how much support is on the grid itself?
I have negotiated 'extra' ceiling wire from the ceiling contractor; it was a worthwile $$$ spent.
Check out Caddy 'IDS' items Independent Support Clips.
