I'm kinda in the same boat as you. I've been looking for a car for about 6 months, and for the first few months all I wanted was a V8 Third Gen. Then, as gas prices continued to climb and me not buying a car was resulting in my finances accumulating, I decided I might be able to afford 4th Gen V6 (There's no way I could afford gas/insurance on an LT1). But after shopping around for one of those for a couple months I discovered they're rare and hideously overpriced, so I'm now back to a V8 Third Gen. And I'm probably be buying an 89 Iroc before Wednesday, so my search appears to be just about over. I hope yours goes well
Bottom line is, if you have the cash for a 4th Gen and you like them more, it's probably better to get one because according to what I've read/heard, 4th Gens are a lot more reliable. You also won't have as much of a problem getting a Fourth Gen as me, as I seem to be in a horrible car market for this.