I'm not sure what you're asking. Are you saying that the P3 1ghz is more stable? hardly. The P3 is sitting at the end of its useful life at 1ghz, it aint going no higher in .18. The Thunderbird, on the other hand, has a lot of headroom left. That alone would dictate to me to go with a Tbird, because you're running much farther back from the envelope.
It says something that Intel had to recall the (whole dozen) 1.13ghz P3s because of instability in certain tasks.