hmm, I wonder what to do with accuracy here. It can be up to autohit player (less Dodgemaster, as it does not involve dice) and normal to-hit vs monsters, or both autohit player and autohit monsters. Enemy damage is not reduced, as it's them who throw damage rolls, not the player, that's the main point of the challenge.
new chainsword 8d2? 0.9.9.5 chainsword is 4d6, and yes, seeing that bulk modes on melee give +1 die to roll (that is, +1 damage in terms of this challenge), and power mods give literally nothing except on shotguns and BFGs, as they add to higher number, it looks like melee will be surely better than anything else. But you can keep pistols to blast barrels, and go rocketjumping like there's no tomorrow.