Visit LS1Tech.com for the skinny on what to do with late model LSx engines.
Tuning software is something you might want to start playing with right now. I like EFILive. Pretty sure they are supporting the new Camaros, but check with them first. You first record WHAT the engine is currently doing, then look for areas to improve. An afternoon at a dyno with a tuning tool can make a significant difference IF you know what needs help.
You can make the car a bit faster by some relatively small tuning changes. The basic timing and fueling is pretty close, so it's looking for "limit tables" that gets the biggest gains.
Do research BEFORE shopping with Hennessey. I'd be careful. There are a lot of reputable LSx hotrod shops out there, not sure that includes Hennessey. He's gets good exposure in the magazines, but his rep on the street doesn't match.
We used to run a 2000 Camaro. Off the showroom floor, it ran 13.85@107mph. By just some minor inexpensive tweaks and tuning (no engine or trans stuff, or weight reduction), we got it to 12.52@111. And that was when they were badged at 305HP/320HP.
Or ....
Get a 125HP dry nitrous kit. You spray it in front of the MAF sensor and the engine will automatically add fuel to compensate. Risky, but lots of folk do it.
