Damage types caused
Guristas - Kinetic / Thermal
Serpentis - Thermal / Kinetic
Blood Raider - Thermal / EM
Sansha's Nation - EM / Thermal
Angel Cartel - Kinetic / Explosive / Thermal
Minmatar Fleet - Thermal / Explosive
Amarr Navy - EM / Thermal
Caldari Navy - Kinetic / Thermal
Gallente - Kinetic / Thermal
Mercenary - EM / Thermal / Kinetic
Mordu's Legion - Kin/Thermal
Drones - EM / Thermal
Khanid - EM / Thermal
Thukker - Explosive
EoM Priests - Kinetic

Best Damage to NPCs
Guristas - Kinetic
Serpentis - Therm
Mordus - Therm & Kin
Blood - EM & Therm
Sansha - Therm
Angel - Explo
Mercenary - Therm
Arch Angels - Kin/Ther

Stacking Penalty: (# of mods, bonus for mod)
1 : 100% (1.00)
2 : 87% (0.87)
3 : 57% (0.57)
4 : 28% (0.28)