Not all cards are created equally, even of the same make and model, hashrates will vary. I've seen as much as 100% hash discrepancies among one EVGA FTW3 1080 Ti Hybrid to another. What you can do is update your drivers, all OS updates, latest mining program, optimize power, core, and memory settings in MSI Afterburner, and be sure they have sufficient power too, say 50% load on PSU is optimal for power efficiency.