Some people will think I'm nuts but you may also want to look at the Federal Assault Ship. It has great armor to start with, so the silent running/no shields thing works very well, it has power to spare, can even be downclassed to save weight. With heat sinks it can be kept pretty cool. It doesn't have the jump range of the exploration dedicated ships however you can carry a big fuel scoop and slap an extra tank in it and still be fully combat prepped. Might be worth looking into as an option if you've got the 80 mil or so to kit it.