The first document makes the choice of pin straight forward. Looks like its RTS then. I re-read the datasheet on the MAX485 chip and noticed something that i didnt notice before. "RO is enabled when RE is low". That helps quite a lot. I thought either RE or DE had to be high to enable either RO or DI. The diagram in the first doc was very helpfull. I thought i was going to need 2 pins from each PIC chip and 2 pins from the serial port for this but it turns out i only need 1.

I didnt see anything about the voltage that comes out of RTS but i guess thats easy enough to measure myself with a multimeter and im guessing its about the right voltage anyway.

Thanx for the help, i think ive got everything i need to know now