I have the 519's (now the 520) on one bike that I use for commuting, and the less expensive 221's (now 224) on the other. Since both bikes are set up similarly, I can interchange the wheels between the bikes (since I agree with Mike about redundancy, although I usually try to achieve it by always having at least two rideable bikes).

It's been my experience that high, even tension on spokes that were properly stress-relieved when the wheel was built is the key to longevity. All four of my current wheels have over 10k miles on them without any failures, and at 210 lbs I'm not a featherweight. In fact, the 221's reside on my heavier bike which, when fully outfitted for the commute with racks, panniers, lights, fenders, pump, tools, etc., easily tops 50 lbs all by itself.

You'll be fine with the 520's as long as the quality of the build is high. No rim will survive bad setup.

RichC