You might find this interesting:
Generally, acceptable load temperatures are 40-65°C, the lower end for Athlon 64, P4 Northwood inbetween, and the higher end for P4 Prescott and Athlon XP.
For P4, as long as they're not throttling themselves it's okay. A lower temperature would help you achive higher clock speeds, but you're not changing that, so it will work just as 'optimumly' in that range. Longevity may change, but you are unlikely to see it fail within its useful working life. As long as it's stable - and you can check it by running Prime95 for up to 24 hours continuously - what do you have to worry about?