The side buttons are different, and the optics are different.
The Diamondback's side buttons are rockers built into the lighted ridge around the sides of the mouse. The Copperhead has four actual buttons, two per side, just under the side ridge.
The Diamondback uses an optical sensor, while the Copperhead uses a laser sensor.
Both mice are awesome. I bought my Diamondback from aspire.comptech, so he definitely knows that they are great. The Razers have a different feel... they are low slung, and longer than regular mice. You control them more with your findertips than your wrist. Plus, the left and right mouse buttons are very long, and extend well up onto the mouse... you can click by twitching your finger instead of having to use just the tip.
My Rig: SABLE
Antec 300 Illusion / Antec EarthWatts EA650 650W / EVGA GTX 760 2GB
AMD FX 8320 x8 Black Edition / Gelid Tranquillo / MSI 970A-G43
Sandisk Ultra Plus 128GB / Samsung 840 120GB / WD Black 750GB / WD Green 1TB / WD Red 3TB
G.SKILL Ripjaws 2x2GB DDR3 1600 - Crucial Ballistix Tracer 2x2GB DDR3 1600
Win7 Ult 64-bit - Func MS3 Mouse - CM Storm QuickFire Rapid Mech Keyboard
R.I.P. Danny L. Trotter
... 14 Nov 1945 - 4 Sept 2009