Using this page for the item attributes:
http://optf2.com/tf2/attributesAmputator361 become fireproof on hit (1 sec) For anti-cave loadouts, since Amputator already helps heal teammates.
Flamethrower/Rainblower/Festive Flame367 - Ext earns crits. Anti-Cave loadouts that would reward pyros for staying close and being a team player. Degreaser isn't used for dmg so it seems pointless to give it ext crits, dunno.
Silenced SMG106 - (15% more accurate)
5 - (15% slower firing speed)
Dunno about that one, but can't think of anything else for it :p The smg accuracy is kind of annoying though.
Holiday Punch176 - Can't be killed with headshots. Anti-CBS loadout that lets hoovies stay in the open at the cost of the running speed from GRUs.