Here's my take:
The only vette that's even close to performance of our Vipers is a '02 405HP Z06 (and there's still a huge difference between the two cars)....so,
Go try to find a Z06 for even slightly under sticker... not going to happen (maybe a smidge under..sometimes OVER sticker). Now, walk or call one of our faithful Viper dealers (Woodhouse, Buhler, to name a few). As Bill said, they'll offer you a very low 5.9% deal vs the bowties 2.9% (that's right, GM is NOT 0% for 5 years...just 2.9%!) .. so the difference is 3%...and I can assure you that their discount on the Vipers will make up just about ALL of the difference in interest (maybe more!)
If it's easier for you to rationalize the purhase at 2.9%, I'm sure Darren (Buhler) or Bill (Pemberton/Woodhouse) will be glad to sell you a Viper at sticker (as you would have to do for a Z06) and then pay down "the points" with the discounts that they normally offer EVERY Viper customer ALL year round, so that you can say you got 2.9% financing.
SO:
$40,000 @ 5.9 = $6287 total interest paid
$40,000 @ 2.9 = $3018 total interest paid
GM dealer discount on 405 HP Z06 = 0!
Buhler/Woodhouse discount on new 450 HP AWESOME SNAKE = (I'll let you figure it out!)
Net discount to you? = VIPER WINS (again!)
Make sense?