If you have an LS, especially one with such a new engine, I wouldn't swap out. I'd test the compression and check if the engine is turbo-capable, and go from there.

And FB's response wasn't asshole-ish... it was realistic. How much money do you have and how much are you willing to spend? What gains do you want to see?

B18C5s are excellent engines if you're looking for massive top-end gains, but I'd like to remind you it's just a tuned B18C1 block with a different head and better cams. With FI and a B18B, some nice numbers can be achieved.