Call Joe Gibbons at Lexus of Chester Springs. I think they can do better. I got my car there in the spring for about $700 over the Edmunds invoice listing; $4500 under MSRP.
Ray Catena in Oakhurst NJ was aggressive in pricing too--I would have driven out there to buy if Chester Springs didn't beat them (Robert Stein, I think was the sales man).
They will ask you if you're trading--answer "No, I think I have a buyer." Get the best price you can for the IS. Once you squeeze every nickel you think you can out of them, say, "What if I traded?" Only do that AFTER you have looked up the price on KBB.com. In SEPA, they will all quote you the "Manheim Auction" price if they are not going to put the car on the lot--they just sell the car to a wholesaler. The only way you can really be successful in bringing them off the Manheim price (assuming they are not fudging it) is if there's more $$ left in the deal you already struck for the price of the IS. You already have something to work with if they low ball your trade.
Chester Springs told me over the phone, sight unseen, they would give me KBB.com price, as long as it was truly in the condition I said. And they did (but not a penny more).