slaughterj has it right. The competition will be perilously close (IMO) if the '03 Viper comes in at 500 bhp. Consider: I've been hearing rumors of 450 bhp for a 6.4 L C6 with a weight of 3000 lbs (from various posts over on the Vette forum -- maybe my info is not totally up-to-date). So, that's weight-to-power ratios of 6.6 lbs/hp for the Viper (3300 lbs, 500 hp) and 6.67 lbs/hp for the C6. Sounds too close for my comfort!
Also, consider this. If the C6 produces 450 bhp out of 6.4 liters and the Gen III Viper produces 500 bhp out of 8.4 liters, the specific output ratios are 60 hp/L for the Viper and 70 hp/L for the Vette. 550 bhp for the Viper would at least bring the ratio up to 65 hp/L. So, I'm all in favor of the '03 Viper coming out with noticeably more power than 500 bhp, otherwise it's going to be very close competition with a 6.4L C6 (if Chevy actually has the balls to produce a 6.4L motor for the C6!!!).
I agree it doesn't seem to be Dodge's style (thank goodness) to come out with performance claims one year and immediately up them the next year. They leave that tactic to GM, which ends up screwing anyone who wants to hold onto a Vette for more than one year as a result.