I've experienced a 10x difference firsthand - and not against bad coders, but against average ones (they were former game developers, so they're quite possibly above average vs. the rest of the software industry). And you can slice the productivity along a bunch of different axes - systems designed and built, loc (not a great metric), complexity, features, etc - and the metrics still hold up.
That said, this order of magnitude is pretty rare (and it was against the slowest of the programmers) - but if you have a few true superstars, you can expect at least a 4x difference against the average in a group.
As far as compensation goes, at my last internet startup there was approximately a 5x difference, once you factor in bonuses. In the games industry, it was more like 2.5x.
For the worst coders, we tended to fire them after a few weeks if they somehow made it past the interview process. So there was a well-correlated difference in compensation there - we either paid them a few weeks of salary or 0$ in the latter case. :)