I'm in the process of designing a Dark Eldar Corsair for my Acolytes to battle with in the current adventure. I gave them a Guncutter ship to fly around in and am trying to determine what stats to give the Corsair. I had a look at the Battlefleet Gothic rules and they mention the Dark Eldar Corsair has "Leech Torpedoes" and a "Phantom Lance." It's also equipped with attack craft and Impaler assault Modules. Does anyone have any thoughts on how to stat these out using the Dark Heresy Vehicle rules? Would this class of vessel be too powerful for a Guncutter to go up against?

Sounds good, but a Corsair is a Dark Eldar escort...  a pack of them can do some serious damage to an Imperial cruiser.  I'd say that's a bit much.  Dark Eldar space craft are incredible quick, nigh-on invisible to standard auspex, and have massive fire power.  They're also rather fragile.  A gun cutter has a snowball's chance in hell of surviving against a Corsair.

Try putting them up against a smaller Dark Eldar craft, maybe a super ravager or raider, which I think would be closer to a Gun cutter in size.  (a raider can hold ten warriors plus crew).  It may be worth it to check out some of the (Dark) Eldar ships on Forge World for ideas.  The DE use ravens and razorwings (fighter jets) and can hire the Vampire Raider (Eldar pirates). 

As noted above, I think an Escort is a bit Overkill.

A guncutter is basically a glorified aircraft which can manage limited inter-system flight, whereas a Dark Eldar vessel as you describe is an actual warship intended for spacebattles.

Go with a Dark Eldar heavy bomber or strike-fighter if you want a fair fight.

Thanks for all your input.