Speaker level and DMX control are two very different things. DMX over proper DMX cable, like Belden 9829 can go ~1500'. If you're using CAT5, it's recommended to keep it under 500' (and additionally, don't use Category cable for temporary DMX cables, only use Category cable in a permanent install).
Speaker cable on the other hand... If you're running a constant impedance system, you can go a few hundred feet with it, but keep in mind you need to run heavy cable (as I said, I run nothing but 12/2 anymore) and you're still going to get a pretty decent voltage drop. My constant impedance speakers that are ~400' out definitely require more gain than one that's only 60' away. It also depends on how much power you're actually trying to send down the cable. If you're trying to power a sub stack a few hundred feet away off of something like a pair of Macrotech 5k's, you best be looking at #8's (of course, ideally in that situation, you're going to have your amps in your FOH rack).
If you go with a 70v system, you can go hundreds, even thousands of feet on basic 18/2 or 16/2 zipcord. 70v systems have the added ability of not needing to worry about impedance, since it's a constant voltage system. The biggest drawbacks are that it's almost always more expensive to do (additional transformers drive the cost up, plus you're paying for "commercial" gear) and it's not always the best for things with low end bass as the transformers can become saturated quickly.
Operations Manager & Technical Director
We're headlining the HauntCon 2012 tour! We hope to see you there!
A big thanks to all of those who came out to visit us on the '09 MHC Pre-Con Tour!