I've driven/ridden in 6th and 7th gen GPs and 8th gen Impalas and N/A to N/A I'd say there wasn't any noticeable difference. Never driven an L67 Impala though, would be weird if there was a difference, unless of course you're comparing a 7th gen GP S/C to an 8th gen Impala S/C, then given then 20hp difference there might be some power difference. I'd take an 8th gen Impala over a 6th gen GP any day though because the Impala has a lot more "quality" interior, IMO.