You will benefit from using this forum's search bar above on the left..... searches there will probe this forum only, which is valuable. Short answer..... those will not work in the xw6400, xw8400, xw6600, but they will work in the xw8600.
Read up on the fact that the processor needs to be approved for use by HP, in their QuickSpecs document. You'll find those processors listed only for the xw8600.
Also read up on the concept of "Performance" heatsinks, and that if the motherboard sees a 120W or higher processor (yours are) it wants a Performance fan, and knows if one is present.
And, read up on my info on how to spoof the motherboard to think it has one of the double tall double fan Performance heatsinks for the xw8600.... you can do that, but don't overdo it.
I personally would advise getting a used xw6600 off eBay, and put in two E5450 processors (which run cooler and almost as fast, and don't need Performance heatsinks). That is what I do......
Oh, and read on how to get the latest sSpec code version of whatever processor you choose to use.
