[jester]

I suggest you go by terms per the rules, but you allocate them more or less generic and base them on their terms in that specific field. I person with two terms as a rifleman will be more skilled in rifleman duties than a one term rifleman and one term tanker, but the tanker will be more diverse. Further a Sgt would be more adept in his craft than a PFC <unless the PFC was a Sgt and was a bad boy.>

Another thing I do, is in order to make the game interesting, having the foe be just as clever and able as the PCs, otherwise the game will get very very boring if the PCs are not challenged.