Its not exactly "replacing" the Xtreme chip. You are paying the extra money not for the speed, but for the POTENTIAL speed on the X chips. (unlocked multi). It is actually the counterpart to the Q9550.
Yea thats what they are now. Used to be both unlocked multi and a nice big helping of 2MB L3 cache. My old Pentium 4 EE 3.4GHz Northwood has 2MB L3 cache and let me tell you it makes a huge difference. Even from a 3.2GHz Pentium 4.
But yea this is just a Q9550. So you can get it now and say you had one first technically.