PWM wire length

How long of a cable can be used for carrying the signal from a PWM output of the Atmega 1280 to the DC-DC converter it controls? Say I'm using an ethernet cat5 cable. I need it to go 30-40 feet. Should I look into a xbee or other wireless solution? I need to control 12 devices.

If I wanted to keep the part count down could I just use PWM signal right from the pin through a patch cable to the input of the LED controller? It will be operating at the default PWM speed of the arduino so I dont really need high freq. Will the signal be OK transmitted over 40 foot of Cat5?

Will the signal be OK transmitted over 40 foot of Cat5?

There is no way of telling because you don't know (and neither do we) how your LED controller will respond to an out of specification signal.
The only way is to try it.