2 royal jelly band, dont feel a difference, besides the defenses dont seem to stack up in total defense
assumptions
armors and other defenses bahave the same way for all depths
robots in advanced training hall deal normal damage
tests
went into training hall with mad bomber set and stone tortoise, 4hits from 1 robot to cut 1/2 hp piece
took off mad bomber and equipped spiral set(proto) as armor and helm, 3hits from 1 robot to cut 1/2 hp piece
took off stone tortoise too and equipped proto shield, just in case it matters, 3hits from 1 robot to cut 1/2 hp piece
results
1.)stacking defenses doesnt matter, its better to mix as many as possible, the maximum dmg reduction seems to be at around 25% only
2.)armors barely help, theyre only good for their bonuses(including health) and looks
3.)HP > defenses
Actually, everything in training hall deals minimal damage. Test again in T2 or T3.