What is the virtue of the weapon loadout? What is the mission profile of this aircraft?
I assume that as a "Strike Fighter" you want an all round craft that can fight air to air but also deliver a respectable air to ground punch - understanding the limitation of mounting armour on a conventional aircraft.
The plasma rifle as a primary weapon is not particularly effective against ASF or DS (about on a par with a PPC), but is a better weapon against many ground targets or conventional aircraft. I would on the other hand suggest an LPL as a weapon that really benefits both from the changes to aero ranges making it a much superior dog fighting weapon against ASF, DS and conventional aircraft and still providing a decent air to ground punch.
Now the disposable reputation of conventional aircraft is primarily based upon its lack of armour and how easy it is to hit an aircraft with close range ground fire or air to air combat, the primary defense against this is not to commonly deploy a conventional fighter in combat where it will be facing accurate return fire - it can however take flak, like an LB-X almost as well as an ASF for a short period.
As such you primarily want armaments or missions that will keep it out of harms way - so, under wing weapons allow bombs and missiles that do not require a low altitude pass over hostiles. For ground attack 10 tons of under wing ordinance from off map or high altitude is the only ordinance you want to deploy against anything likely to return fire (such as battlemechs or tanks)
Against air to air targets I would want long range to minimise return fire - maybe something to force control rolls - a pair of LRM5 with a ton of ammo will serve me much better than a few RL20 and if I sufficiently outnumber the ASF I can fly defensively, avoid close range shots and plink away hoping to force them out of control
That still leaves me with 2.5T - so how about 4 LMG and half a ton of ammo - infantry are mostly unable to return fire against aircraft and a good strike into an isolated infantry platoon could easily cause significant casualties while staying out of the main fighting. Extra short range firepower might occasionally hurt an air opponent too
