For UDMA33 you don't need 80pin cables, UDMA66 and up requires them - but it doesn't hurt. I've had cables doing PIO4 and MWDMA2 (16 MB/s) reliably but no UDMA33.
Looking at the price of 80pin cables, I replace 40pins whenever I put my hand on them.
Lacking YUV overlays explains the problems you're having as DIB DRAW incl. conversion is a pain in the a** for the CPU.
The Riva128 should be able to do YUV overlays, but I'm not 100% sure. Maybe I'll check it in a couple of days as we're just revamping an old RC440BX system, it's got a Riva onboard. ;-)
What drivers are you using? DirectX in good shape?