Excuse me for my noob-ness, but what exactly is the "link-bank-fire-penalty"?
What Aesaar said - when you link the gun banks in your fighter, the fire rate of each individual bank drops. Total DPS is still higher (IIRC) but not as high as the summed DPS of the individual weapons.
Actually depends. Sometimes there is no benefit, or it even lowers your DPS.
Linking a 4+2 bank is the same as firing just the 4 bank in terms of DPS. Thus, there is (little to) no benefit in carrying the same weapon in the 2 gun bank, use it for a support weapon. I say little, as the increased burst damage for the same DPS can be beneficial if you have good aim and need to punch through shields or such, but generally you're better off with RoF over burst damage.
AFAIK, it's a ~33% decrease in fire rate when two banks are linked. Not sure about three. So, linking say, a hypothetical 5+1 would actually give you less DPS than just firing the 5-gun bank by itself (!)
Of course in reference to this thread's discussion 2+2 obviously does give a benefit over just 2, but it is markedly less effective than a plain 4, which is equivalent to say, a 3+3 (or any combination of 6 guns total).
All in all it is an interesting dynamic which is very much so a part of the FreeSpace universe and removing it would throw off a lot of players who expect it, especially in a FS-universe mod.