I did it the other way around:
4 fixed pulse or burst lasers in the small slots for shield crunching or small enemies
2 fixed Multicannons in the medium slots for large targets hull.
Why all fixed? Maximum damage. Large targets (Clipper, Python, Anaconda) have sufficient area (if alinged properly) to hit with all fixed weapons at the same time.
While your thrusters are not fully upgraded, gimballed lasers might be better.
Rail guns in the medium slots are fun too, but fight for cooling capacity with the lasers-->firing all at once is not feasible.
Regards,
IceFire.