Well, I can share your pain and would say that the wait will be well worth it. My car was out from October 28th to January 4th. I would guess that Arrow had the motor for 5-6 weeks and the dealer had a couple weeks on either end to get it in and out. I am told that Arrow is sometimes backed up a little in the winter months, as many wait for warranty work when the snow flies, as I did.
Now, while I can share your pain to a degree, I would think you could expect a few more problems buying used rather than new. Granted, most will be pretty much problem-free, but it is generally difficult to tell what the car did in it's previous life. Sure, you can do a Carfax or other similar look up, but it still doesn't tell you how the car was treated. While I wouldn't hesitate to buy a used Viper under warranty, I probably wouldn't do it otherwise (that's just me). I think you are fortunate to have the warranty and you will be very pleased with the results. Arrow does a great job and I am VERY, very happy with the work they did on my car.
I would assume that the times you have been in the shop previously were engine related. I believe that the warranty from Dodge specifies that the ONLY place you can "crack" the engine open is with Arrow. I don't think they even want their 5-star dealers doing anything more than removing the valve covers. I may be mistaken, but somebody else can better address this. While it is a mild pain, the alternative is to possibly screw up a $10,000+ motor. I would pace the floor and read this board for your fix as I did. You will be thrilled when it is back and should have a GREAT summer with one of the greatest cars ever built. Enjoy!
Chris