Small update:
Drove them both Saturday and got some good 'fun time' behind the wheel on both. As expected, the manual in Z06 didn't disappoint in the fun department and it helped to give it a feel of more torque over the automatic '05.
The '05 though...it didn't disappoint even with the automatic. Everything just seemed a bit tighter and more 'put together' in it.
After we spent the better part of the day goofing around in these and pretty much pretending we were on Top Gear, what we discussed at dinner pretty much sealed the deal for me.
He let me know that he's going to sell the '09 Z06 no matter the length of his stay overseas. As I let him know $20k is my threshhold right now for another toy, I'm going to get the '05 convertible for now and we will work something on the '09 at Z06 a later date.