I've read comments that the stand you're thinking of (Quik-Lok WS-540) is rather sturdy, and that the more weight you put on it, the more stable it gets. rmbaylin and I discussed its pros and cons earlier in the thread. Quik-Lok sells this as a speaker stand; it's intended to hold house speakers up to 300 lbs. It might be worth a shot.
I wound up going with an Ultimate amp stand (I found a used one at Music-Go-Round at a price I couldn't pass up). It's only a three-point support, so I have stability concerns, but it turned out to be more stable than I expected, and it's low enough to the ground that if my rack does take a spill, at leats it's not going far. I might have to gin up someting like bluesdoc's booster, though, because I have to bend down a bit to reach it while standing. I did have to cut some metal tubing to extend the support bars to span a 4-space rack case.