Something to keep in mind from a handling standpoint besides weight, is weight:wheel ratio. 1LE for example - ~3850lbs., but it has 10" and 11" wheels - total weight divided by total wheel width is 91-92lbs per in.
Current ATS has 8's and 9's - to have the same lbs/in, the car would have to weigh 3130lbs.
A real win would be decreasing weight (especially front weight), decreasing overall size (including wheelbase), maintaining or increasing power, and not hamstringing it with narrow wheels. Good width wheels are a key element of the current Camaro having fared so well in its various handling-based matchups; if the 6th Gen loses 300lbs. but gets the ATS wheel widths, it will probably not possess the handling limits of the 1LE+ class 5th Gens.