from my experience the acheron is not very good, since it packs too little punch for a heavy cruiser. ranges are nice though. but still very stylish.
devastation class for 190pts is a must have. 4 squads of ordnace for under 200pts is unrivaled.
carnage is the one and only eldar killer. versus other fleets it performs averagely. solid ship. but 2 of them is too many for my liking. what i've seen working with brutal efficiency is a squadron of 3(!) teamed slaughter class cruisers. they outrun every other ship at breakneck speed and pack a short range punch similar to a retribution class battleship. just head straight into the enemy or go over a flank (they can do this in one turn less than any other imperial ship!) and watch the massacre. and they virtually cost no points. 165pts phhh.. wtf?
idoators are superb escorts. but you should consider to include some infidels because of the torpedoes. remember: turrets cannot fire vs normal ordnance or torpedoes in the same turn. if you combine a salvoe with a bomber wave you will get some nice results :grin: