I don't currently own a 4th gen, I own a 3rd gen (you can look at my build thread in my signature). I don't think you can go wrong with a 4th gen V8 at all. I've been seriously thinking about selling my 3rd gen to go with a V8 4th gen. After all the reading I've been doing I'm pretty much convinced on it. This is my set of criteria I'm looking for in a 4th gen when I look. I typically look for 2006-2009's, but if I find a 2005 for the right price I wouldn't mind it. I want a 4th gen under 50K miles, but that's asking a lot. The closer the mileage is to 90K I would start looking for the timing belt being changed. Other than that, I don't think there is a whole lot. Take a look at this thread:

4th Gen Common Problems Question