I'll agree that a used Z is a pretty good deal especially if you can find one for under 40K but it will most likely be a 06 or 07. I got my base model 08 for under 30K. I could have went with a Z but I wanted to build a boosted LS3.

 

I would have a hard time not picking up a lower mileage LS2 or LS3 C6, you can get those anywhere from the low 30's to high 20's all day with relatively low miles. I have heard many negative things about the LS7's and their durability, especially when it comes to adding any kind of power to them. Plus the Z06 really only has an advantage in terms of dollar to performance up until a certain point over the others. So, despite the appealing price of the used C6 Z's, I really would have to think hard about jumping into one versus when of the LS2's or LS3's.