you cant compare a car you see everyday (S197) to something that is hard to see on the road (SRT8)? track times are similar. a few tenths mean nothing on the street. if you raced a S197 and got beat, you cant beat a SRT8. if you beat the S197, then it would be a good milestone to judge the outcome.
the srt magnum runs slower times then the srt 300 and charger. most likely due to weight. that is probably the high 13's you saw for the magnum. the other two cars will run under a 13.5 every time.