stock v8 is 426hp and 402lb-ft
this one is 562bhp and 557lb-ft
Detailed differences/additions are as follows (source: Hennessey website):
2010 HPE550 Camaro Package (available for 6sp & auto)
Power:
[*]562 bhp @ 6,200 rpm /li
[*]557 lb-ft Torque @ 4,200 rpm 


Performance: /li
[*]0 - 60 mph: 3.6 sec. * /li
[*]1/4 mile: 11.7 @ 121 mph *
* Performance numbers obtained with optional 20 inch drag radial tires and wheels.
Includes: /li
[*]Magnuson / Hennessey Supercharger System /li
[*]Corsa Stainless Steel Exhaust System /li
[*]Hennessey Air Induction System /li
[*]Hennessey High Flow Fuel Injectors /li
[*]Hennessey Engine Management Calibration /li
[*]Hennessey Aluminum Wheel Upgrade (uses factory tires) /li
[*]Hennessey Cam-Aero™ Urethane Body Components: Rear Lip Spoiler, Front Splitter & Side Rocker Panels /li
[*]Hennessey Exterior Graphics Package (rear quarter panels) /li
[*]Hennessey Premium Floor Mats /li
[*]Hennessey & HPE550 Exterior Badges /li
[*]Serial Numbered Plaque in Interior & Engine Compartment /li
[*]3 Year / 36,000 Mile Limited Warranty /li