They are better sprinters, in the long run, you will be faster thanks to the larger engines. Don't let them get somewhere where they can use their nimbleness to their advantage! And to answer your next question, no such area is close by. The problem is that you're one ship and they are four. They can split up easily.
I'm dubious that the pirates/smugglers would be fleeing from an abandoned wreck, so yes. Also, abandoned wrecks don't tend to come out of the Warp except as portions of a Space Hulk.
You've been spotted as you can guess from their sudden turn and running away from you. It is also not hard to miss your arrival. You left the Warp (big spike on any Augur) with running engines and reactors. To put it simply, any ship with even a half working set of Augur Arrays can pick you up. It was them, that had powered down their reactors to a degree that made them almost invisible. But you have better Augur Arrays and they got lazy in there camouflage skill.
Yeah, but these are tiny pirate ships, we can only carry so many torpedoes, and we still have most of our patrol to do after this encounter. Best save them in case we come across an Ork Kill-Krooza or a small flotilla of Chaos raiders. Or Eldar ships.
