the 16.6MB/s isn't a problem, that is fast enought for all burners.
the minus of PIO mode is that it uses a lot of the CPU. in DMA modes (Mult-Word DMA, UDMA) the CPU usage is much lower, and that is why you can burn at faster speeds.
like cfitz said, it's best to avoid PIO mode if you can. Multi-Word DMA is better, UDMA is best.
it think it came out in the other thread, that the SIS problem appears (apparently) only with Plextor drives or maybe just this model.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the land of Mordor, where the Shadows lie
M.C. Escher - Reptilien