dont do missions. ever. unless your re-fixing, dont ever, ever do it as a way to make money. they just frustrate me, and it seems your the same way. get a transport and look for a trade route. i have a 30|10 route, at least i think thats what it is. about 30 minutes for 10 mil. by the way, what ship do you have? i would just RP and help in battles with a capital.
Hmm on a corsair bomber of my i made like 30 mils an hour doing missions so missions is a valid way to make credits.. and one more thing.. they should make more.. we had a talk about this... when you do missions against BS's you should be rewarded more.. as a lone BS cannot take on 5 other BS's and a lone bomber cannot do that as well.
So say a hard mission will make more credits.. but the answer was "more missions= more NPC's = More lag"