The ACR is about track performance, as in a road course.
A GT500KR with 725 hp (and solid rear axle, 4,000 lbs) vs a 600 ACR on a road course, no contest, I'd love to take that race against the GT for pinks ... cause I'd love to have GT500KR.
Guys are running 550-600 rwhp in the GT500s and only turning 120-125mph in the quarter, these things are 2tons (of fun), but still, a pig. Understand, I've had 6 stangs since '87, 4 Cobras, I have an 03 Cobra Terminator with 523rwhp, but it's no match for my Viper, but these are 2 very diff't cars bought for different reasons - I'll have a GT500 next year as the prices are finally now running at MSRP.
As for the hp wars, frankly to me it's a poser battle, like your cars hp is in correlation to you penis length or something. The Viper is about more than just posing with a big number, IF the vette comes with performance that requires more Viper power - well, there's the Mopar option for 75+hp, and Dodge is watching & will respond with more if needed, as they have before.