Hmm, just increase the pixel clock to max and set the resolution to the native of the TFT.
The chip is so slow, that you're not in any danger of blowing the TFT - lucky if the refresh rates are good enough for it to sync. Mine goes down to 50Hz, so no problems there.
I'm running CGX, not P96, but the fundamentals are the same.
Thankfully the TFT isn't as fast as a monitor, so you can get away with the lame vertical refresh rates the Cirrus Logic chip gives.. I wouldn't dream of running 1280x1024 on a CRT with the PIV..
Almost any card released in the 2000s (like your voodoo) will be able to generate nice frequencies, but the PIV's chip was not top notch even when the card came out.