Thanks for all the input. Mr. Dudley's car is, to some degree, what generated the initial discussion.
My 91 928 has a 4 speed auto with a 2.54 final drive. I've never actually driven my car so with my block back from the machine shop, I've been thinking about what do with the car after I rebuild the motor. That means I had to drive some 928s.
Drove a 90 S4 that the owner, a Rennlister 928 enthusiast, kept up mechanically but was cosmetically horrible. That car made me want to never drive a 928. It was incredibly slow...my 94 E320 is quicker. And while he said it had new rear shocks, the car rode like it had 10 year old tires and the shocks were frozen. The rear hatch rattled like it was going to fly off at any second. It recently sold on BAT for $9100 or so. Horrible car.
1990 Porsche 928 S4 | Bring a Trailer
Then I drove an 87 5-speed S4. Taking on and off ramps, respecting that it’s not my car and I didn’t know the tires, was intoxicating. Effortless speed through them. It drove like a 928 should with bank vault like solidness. I fell in love. An 87 has a tall 2.20.
But that car made me realize that if I want to keep my 928, I would have to make it a 5-speed.
With that in mind, I did some research and the only transmissions worth putting into it would be the 2.73 G28/10 in Mr. Dudley's car or an uber rare G28/55 found in 89-91 GTs and the 88 Club Sport. I have found one, in fact it's part of an entire conversion kit.
I am driving a 91 S4 auto in pristine condition tomorrow as a reality check.
I do have access to a 90 GT with the motor in pieces so in theory I could rebuild my motor, put my car back together, sell it and buy the GT and rebuild that motor. Then I'd have a truly collectible 928 with a 5 speed. But I'd also be rebuilding another motor.