03-06 was 500-510 HP, depending on what formula was used (03-04 says 500, 05-06 says 510...same engine!). 05 did have the Copperhead edition...no extra power, just trim and paint.
You are close but let me throw in a few more facts.
The 05-06 engine has knock sensors allowing for a little more tunning, that is the difference.
The Copper color as you asked about earlier was only built in 05 on the verts and they are numbered special edition cars called Copperheads, they only built 300 of them and all came with a numbered badge on the console. Besides the fore mentioned trim witch included special orange stitching in the seats, shift boot, steering wheel and floor mats you got the very sought after polished side winder wheels. These wheels were only available on these 300 cars. It is the same wheel that is now black on the 08-09 ACR's and they are the lightest wheels you can get for a Viper.
They also built 36 2006 coupes that were the same color but they did not come with any of the other special features the limited edition 05 Copperhead edition came with.
I have a Copperhead, it was pretty hard to find a decent deal on one. Most of them you find people are asking a hefty price for.
Whatever car you do decide on make sure you have a pro check it out for you. There are way to many Vipers out there that have skeletons in the closet.
Let me know if you have anymore questions, and good luck!!