For example digital pin 10 shows (PCINT6/OC1B/OC4B/ADC13) PB6 I assume that "OC1B" tells me it is timer 1, or is it timer 4 (OC4B)??
Both. You can configure this pin to be altered by either timer 1 or timer 4.
My second question is how to work out what prescale factor to use and what settings are available.
The prescaler defines the PWM frequency while the OCRX(AB) register defines the pulse width. The value of the prescaler says how much clock cycles it needs for the timer to be increased by one. An 8bit timer counts from 0 to 255 and back again (in PWM mode), every time it matches the value in the OCRX(AB) register, it toggles the corresponding output pin (if it's configured so). This results in the simple formula for the PWM frequency:
clock speed / prescaler value / 2
in the example:
16'000'000 / 256 / 2 = 31250Hz (not kHz as in your comment)