Gromacs vs lammps

I mean, if Lammps is faster than gromacs. I am doing simulation on polymeric system. Right now, i am running simulation on approx 1/2 million atoms, speed on gromacs is 22ns/day on 160 mpi ranks, 20 cores/node, intel ivybridge . Thanks alex for the suggestion, i will try to do some bechmark test and try to inform you.