I would perhaps instead of the arduino's driving the servo's consider something like an adafruit 16 channel servo controller.
By playing with the prescale, I believe you could get the desired servo frequency.
Then it is just a question on how fast you can get the i2c data to the servo controller.
There is somewhere a variant from another manufacturer (in the UK I believe) that uses a secondary external crystal on the controller chip (Can't for the life of me remember which chip it is). ANyway the external crystal is supposed to be more accurate.
I have just submitted the upm libraries to Brendan for the adafruit controller so hopefully they should be in the dist soon - these are not however arduino libraries - but from memory, I think the adafruit libraries will work on the Edison with little if any changes.
It would seem that this might solve the PWM issue - I'd need 2 however, only running 8, as to send all 16bytes to one arduino over 8.3ms results in a serial buffer overflow.
Even with two, the input serial rate is still an issue ...
Maybe I could have mentioned this earlier but the sensor that the PC is working with only gives at most 8bits resolution anyway, so, in addition 12bits would unfortunately be wasted on me
Still though, it's nice to know about the product.