I have had 3.5 for quite a while. I used it with my A3000D, but never on the 4000. I recent sold the 3000, and decided to "upgrade" the 4000 a bit. So, I just needed the ROM's to install OS 3.5.
I've gone back to 3.0. My 5 gig drive is back to 2 gig (2, 1 gig partitions) and I'm reloading all my software.