I don't know if this is helpful, but some time ago I tried to get 1680x1050 working on my A4000T with Voodoo 3 3000.
Here is the link to that thread. I was apparently successful at getting the card to run at that resolution, but the display thought it was running at a different resolution. I eventually gave up, and moved the entire system to the computer room where I hooked it up to a 1280x1024 LCD and forgot about it :-)
I had problems with my system locking up after I installed the Voodoo card. I first did a disgusting kludge of taping (yes, taping) a cooling fan to it, which worked but the fan kept falling off. I installed a slot cooler below the card, and this fixed the problem for me.
