I finally got my stealthy assassin up to level 100. It's a 250 Tactical / 200 Command / 50 Helm ship. No mods.
It is ridiculously effective. I do not bother to cloak unless I'm fighting a race ship or a boss, because the laser/virus combo blows up monster ships in a faction of a second.
When I do cloak, the stealth bonuses last for six seconds which are enough to kill three race/ancient ships, or two Talon/Overlord/Legion ships. Once the bonus goes away, it is trivial to get some distance away from any surviving enemies, because the fighter screen keeps them busy.
The screen shot is taken while cloaked, of course. Note the attack. critical hit chance and direct hit chance. There are no misses, every hit is a critical, and half are for max damage, which makes a big difference, with beam weapons. The effective DPS is actually at least four times the displayed one.