Peasant w/ full iron armor and steel war hammer vs peasant w/ full iron armor and platinum war hammer (test ran twice):
69 group 1 survivors
131 group 2 survivors
Density definitely has an effect, but it's not huge (platinum is something like twice the density of silver and only made the hammers slightly better). Also, slade now seems to be unavailable in the testing arena, although I suppose I could just mod something to have similar stats.
Peasant w/ iron scourge vs peasant w/ iron battleaxe (test ran twice):
106 group 1 survivors
94 group 2 survivors
Scourges are about even with battle axes for unarmored combat, but if you give them armor scourges will penetrate while battle axes won't, resulting in a 100% victory for the scourges. Note that scourges are edged weapons, so they're like knife-flails or something (and they're made out of metal, not leather, resulting in many flying body parts).
Peasant w/ full iron armor and iron scourge vs peasant w/ full iron armor and iron whip:
33 group 1 survivors
67 group 2 survivors
Whips are blunt weapons, so they're better for armored combat than scourges. They can't sever, but they are very, very good at chipping bones, which tends to cause extreme pain and thus allows for instant kills when enemies pass out from the pain.
Peasant w/ iron scourge vs peasant w/ iron whip (test ran twice):
111 group 1 survivors
89 group 2 survivors
This follows the general rule that edged > blunt for unarmored combat, and blunt > edged for armored combat.