How about just a straight Rog16?
Five feats: Weapon Focus (Shortsword), Weapon Finesse (Shortsword), TWF, ITWF, Improved Initiative. Take Crippling Strike as one of your three Rogue special abilities (Slippery Mind and Improved Evasion are also nice abilties, but not so relevant to the Sneak Attack discussion.)
Wear a Cloak of Displacement - you won't be able to get your AC up high enough to matter against big foes, so just make half their attacks miss.
If you surprise an opponent and win initiative you can get half a dozen Sneak Attacks in before they can even act (and with II and, say, 28 Dex based on starting Dex 18 with racial modifier, 4 stat raises and a +6 item you'll have a +13 Initiative modifier....) Each Sneak Attack can deal 1d6 + strangth + magic + 8d6, or about 35-40 points of damage + 1 point of Str damage per strike.
You will need flanking partners to deliver Sneak Attacks against opponents who are aware of you, but other party members or even summoned creatures can serve that purpose.