Worth noting, but the actual decision of what ship to board is going to be Vedius'; whilst we should pick a ship to board, it ought to be based on Vedius' mindset of "what is a good ship to board and how". That said, a random Eldar ship winds up being a definite "no" in this situation, since there's no real way for Vedius to know that anything along the lines of the plan Necroes has suggested could be done, and I imagine even if he did, he'd rather object to turning hundreds of sentients into Chaos Spawn like that. I figure it's far more likely for them to just go ramming speed into an Imperial ship's bridge, take the bridge hostage, and commandeer the ship via suitable "persuasion" of the captain, whether social and subtle, or "I will mind control your brain directly via technology". 99% of the crew never even has to know they were boarded, on account of 99% of the crew doesn't work on the bridge.