Yep, it is a whole different car. In the C5 they just did, heads, cam, exhaust, wheels, scoops. to a stock C5. The new C6 Zo6 has the 427, brakes, wide body kit etc...
Yes, Terry is right... the C5 car was an upgrade over a stock C5, but nothing like the difference in a C6 vs. Z06 now. Also, the C5 Z06 stickered for ~$50-51k, which was still below a fully-loaded C5 'vert at the time.