I purchased my first Viper using a Credit Union Loan, good terms and rate..... but if you really need to finance it out that far, and you are doing that on a bottom dollar Viper (likely out of warranty, with miles) I would be very careful if I were you.
Not trying to be pessimistic, but 30K @ 10% for 5 years is a $640/mo. payment vs. $750/mo. for 4 years. If that $110/mo. is the difference between you being able to afford the car or not, the first time you need to put tires on the car, you'll be hurting. You need to be able to enjoy owning the car, and if there is not enough free money available to take your wife out to dinner on Fridays, you will not enjoy your Viper.... trust me on this one
I am seeing some tings start in the Viper market that are similar to what occurred in the Jag XKE market in the late 60's. People can afford (?) to buy one, but not own and properly maintain one. Have you checked insurance costs (can be $200/mo. if you don't have a clean driving record, even clean $100.mo. is realistic)? Does it need a set of tires (Cha-ching, $1200)?. Be careful and patient.......