I've seen hobby projects (usually from hack a day) with pixelated LCDs that are controlled by microcontrollers (~16MHz). I've also seen a lot of larger TFT screens (usually in tear downs) that used 200+MHz ARM controllers.
Since most pixelated LCDs use controller chips, does the size of the LCD determine the frequency needed to control it? If you see an LCD of a certain resolution, can you get a feel of the required processor frequency?
I guess it would depend on the controller chip, DMA controller, etc. Hardware acceleration would make it less dependent on the processor frequency. Of course, if there is alot of "real" processing, rendering and such, then the processor speed would be more important. Too many variables for me to think about.
Juts google for 128x32 or 128x64 LCD module, they are getting pretty cheap now and they have an onboard driver so you control them with about 12 PIC pins.
You don't have to do any frequency stuff, you just tell it the byte to draw on screen and where to draw it.