I agree with PianoMan, but I need to advise as follows.
The XP-120 was top-of-the-market when people were using either AMD processors or Intel Northwoods.
You could OC a Northwood 3.0C to 3.6 Ghz with the XP-120, and expect at most a 15F-degree spread between idle and load temperatures. For the same hardware, we swapped out the XP-120 with an SI-120, and the idle-to-load spread was closer to something between 6 and 8 F degrees.
If you want to dump the E6600's stock cooler, then you must also be thinking to over-clock the processor -- unless -- unless -- you've got case-ventilation problems and hope to mitigate them with a more efficient cooler. I'd advise, if such is the case (pun), that you resolve that problem by improving the case.
If indeed you're planning to OC, I cannot say that I have the numbers at the tip of my tongue to tell you that the XP-120 is adequate, but I would advise you to consider either an Ultra-120, an Ultra-120-Extreme, or an Ultima-90. You could also get by with an SI-128, but I suggest you use it as an opportunity to duct the air onto your motherboard and out the rear of the case from the underside of the cooler.
There are other coolers which are adequate to over-clocking the E6600. However:
Big Typhoon comparison review -- >> ThermalRight rules
and:
May 07 "Update" to ThermalRight Ultra-120-Extreme Review -- >> ThermalRight Rules
A careful inspection of the graphs beginning on these pages should suffice.