GACK!!! That's the same old tripe my old 'fritter buddy Chris Lawson & co. over at LEM were pushing back in the day. OF COURSE PDS video is faster than NuBus at the piddling resolutions and bit depths it supports. However . . . that I/O bottleneck is a moot point . . .
. . . Apple NEVER BUILT A PDS BASED VIDEO SUBSYSTEM WORTH A DAMN for anything over the middling size resolution of their 16" Monitor spec during the entire 68k era!
If you're doing PhotoShop, a NuBus Card driving a TPD @24bit with four DSPs on board pounds the snot outta the 840AV's onboard video and single DSP. The MoBo video is fine for palettes, fast for gaming and great for tiny Video window playback . . .
. . . but it takes a gnarly NuBus card to do Photoshop justice. :approve: