Installing WB3.9 over WB3.1

[Oldsmobile_Mike]

Personally I prefer a clean install in those situations.  Boot off the 3.9 "emergency floppy" and it's pretty straight-forward after that.  Mine had no problem finding the CD-ROM and installing the rest of the OS from there, after that I immediately installed BB 1-4 and various other library updates (Peter K icon library, Cosmos's and THoR's updated libraries, etc.).  Now on this board you'll get some mixed reviews of BB 3-4, but IMHO I like to have the most updated system possible, and didn't have any issues with them.  Your mileage may vary.  

[Oldsmobile_Mike]

Probably a dumb question, but why would anyone want to use 3.5 instead of 3.9?  Not that I ever used it (skipped right from 3.1 to 3.9), but from what I recall it looked kinda just like 3.1 with NewIcons slapped on.  All the real benefits came with 3.9.  

Also just a quick Google search, it looks like Versalia and other shops still sell 3.9 for quite a reasonable price, IMHO.