I benchmarked...at its top temp, using 100% of the cpu, it hit 54. I'm not sure if that's "dangerous" but I figure buying a new heatsink wouldn't hurt...do any of them work specifically well with p4s?
SuperPi, Orthos and Prime95 are also good stress testers, but only Orthos is dual-threaded.
54 isn't too bad for a full load, so I guess you're ok. If you're still looking for a good aftermarket cooler though, you can pick up a mid-range Zalman or Thermalight. The Thermalight passive coolers are actually pretty effective, and you can hook up a small fan for some easy cooling.
