39cent, why would be any different because of using a cat5 cable? One is the spec. of the protocol, that states to which distance it must work perfectly, and another thing is the actual usage.

The answer, pretty long distance. And if it's too little, grab a 232-422-232 converter, (232 and 422 are not too much different), then you're ok for 4000'. One good trick would also be to balance the rs-232 communication, just put 2 transformers 1:1 on each side, and run the balanced signals in a twisted wire pair cable (cat5), in the same twisted wire. Should lenghten the distance of 232, the problem might then be the MAX-232 IC to drive a long line like this (and transformer), but there should not be too much problems.