Oolite Bulletins

Just wondering, does slowing down affect the rate you can turn at? Is this why NPC ships spend a lot of time going slower than their max rated speed?

I don't think speed effects turn rate, per se; the max thrust used to turn remains the same.
Speed can effect the tightness of the turn, though; The faster the forward velocity, the wider the turning circle. Watch NPCs with the injectors burning try to make a hard turn, and notice how wide that turn is. Meanwhile, NPCs that cut the throttle back manage to disco all over, pulling sudden and quick evasion turns.