I vaguely remember building a Lenovo M58p, I think it was...and wasn't able to get a modded 771 Xeon to work in it. QX6700 was what I ended up getting, I think...or maybe it was just a tape modded Q6600. This was quite a few years ago now and my memory hasn't been the same since I was hit by a car. During that time though, I was putting modded Xeons in everything, so I am nearly positive it didn't work, for whatever reason. I still have a couple of X5450 sitting around...if someone here wants them, PM and I'll probably send 'em to you. They probably don't have the stickers though.
EDIT - nevermind, that was very likely due to chipset...and 65nm <1066 Xeons weren't worth it over a tape modded Q6600 / Q6700 on the Q45 chipset. Are you having issues running one? What system(s)?