[Dx-qsl] When does it make sense to mail directly to an incoming DX bureau?

Tue May 16 11:10:10 EDT 2006

This has probably been discussed before so my apologies in advance if it 
has, but when, if at all, does it make sense to mail directly to an incoming DX 
bureau?

I use both ARRL and WF5E and was curious, is there a weight threshold (# of 
cards as a rule of thumb) that applies visa vis ARRL or a 3rd party service? 
What postal service is used, airmail post, surface post?

Bill
K3WI