Do you mean the TT120, as in the Tuniq Tower 120? If so, that really isn't necessary for the X2 4000+. The Arctic Cooling Freezer 64 Pro is sufficient.
You mean idle? Well 40 is a good temperature for idle. But I can assure you, that the ACF64 Pro, is good enough. But if you feel that you want a Tuniq, be my guess. Your choice, not mine.