I've tried a lot of FDL loadouts in the Beta, the class 4PA is huge fun if you hit an unsuspecting Sidey or Eagle but once they start maneuvering it's extremely difficult to land a second hit, same for the class 4 cannon so unless you're going to hunt big ships they're not great as general purpose weapons.
With a 6A PD delivering 50 MJ energy to weapons this equates to around 3 MW of weapon power, you can draw more power but the weapon cap will drain much quicker this limits the weapon fit to either pulse or beam and kinetic, the biggest laser weapons on the FDL will 4 x class 2 and 1 x class 3 (no class 4 in game ATM)
FDL beam/kinetic, great fun but ammo limitations will mean regular returns to a station for rearming, small beams to keep mass down and reduce overheating issues.
http://coriolis.io/outfit/fer_de_la...4d0303242h.AwRj4yrI.Aw18cCMxA===?bn=FDL basic
FDL all pulse, what I'm currently flying, you could add a class 3 pulse on the belly mount, but as it's not going to fire all the time due to it's location it's just additional mass you can do without.
http://coriolis.io/outfit/fer_de_la...0303242h.AwRj4yrI.Aw18cCMxA===?bn=FDL basic L
Better shields, thrusters or SCB's you'll need a 5A power plant and you'll soon run into power/heat issues, perhaps a missile rack in the belly mount is worth a try although it takes 2 rounds to kill an unshielded Sidey.
The new FAS in the next update is a ship with a lot more loadout options but it's not that fast (boosts well though) and the shields aren't fantastic but it's fun to fly with minimal power issues, I do like the FDL it's huge fun to fly and sounds crazy but it's a frustrating ship in some respects.