My own experiments with OC'ing my X2, and from what I read, suggest that the limiting factor for how far you can push it is not really heat-related. My 4400+ craps out long before heat becomes an issue. Obviously cooler is always better, but I really don't think heat is a big factor because these chips really don't get very hot. Rather there is a threshold for each chip over which it rapidly gets much harder to OC. As such, I think any decent hsf will do the job.
The BT is just waaaaaaayyyyy OTT. Save it for your dual core Pentiums! And I advise against the Thermaltake CL-0092. Again, my experiments suggest that fans in funnels don't work very well due to air back-pressure issues.