Xeons are stable but of no real use to most folks. Their RC5 output is identical to its counterpart at the same mhz. For example, the 400 mhz Xeons I use at home only put out as many RC5 blocks as a plain old 400 mhz CPU. The 1 meg L2 cache on each CPU I have never comes into play.
The ones I use at work are the same way. I just needed Xeons for database work and a few other programs. RC5 cracking is just a happy way to use any wasted cycles, they all run 24/7 anyway so why not?