I'm not familiar with the lowering kits (yet), but I'll throw in some advice that you may not want to hear. If you don't like what I'm saying, that's fine, I just want to let you know what you're in for.
If you're lowering for handling, don't go with 20" wheels. They're heavy and the lower profile tires will kill your ride. Also, you'll lose handling capability on any kind of rough road. Smaller wheels with fat sidewalls have more ultimate grip with less responsiveness. Larger wheels with short sidewalls don't conform as well to rough surfaces but 'feel' more sporty.
Camaro wheels aren't a bolt-on. Our trucks have the 5x5 bolt pattern while newer Camaros have the 5x120mm bolt pattern. You'll need adapters, which add even more unsprung weight.
The majority here will tell you 4/6 or nothing, and I'm in that camp. A 4/6 drop won't put it in the weeds and a 2/4 looks almost stock to me. Whenever I get my 1-ton up and running I plan on putting a 5/7 drop on my stepside.