Bingowings is correct. When the Quadrilogy DVD set was being assemble Fincher flat out refused to do a Director's cut. Even Ridley Scott did a Special Edition cut for the set but set the original version was the Director's cut and superior.

Fincher just never got over how they treated him while he was making the film.

As far as an uberedit goes, I did work on one for awhile. What I discovered is that the differences between the 2 versions is just to great. As soon as you start adding content from one into the other you create discontinuities in the plot. Swapping the dog burster for the yak is about the only change you can safely make between them. (And IIRC that causes a few problems as well.)

I don't believe there was anything in the workprint that was useful that didn't make it into the SE.

The Special Edition cut is probably the closest you'll get to a completely complete version. I know it completely changed my opinion of the 3rd film (I almost didn't buy the set because I had no interest in ever watching Alien3 again).

Don't let me dissuade you if you have a plan though. If you make it, I'm sure I won't be the only one who'll give it a watch.

Which reminds me, I really do have to work on my shelved Alien 4 edit.