[Spambayes] more testing: spam/ham proportions?

[Anthony Baxter]

Ok, as well as my humongous test set, I've now got a largish collection
of spams from the last couple of weeks, and I'm about to pair them up 
with randomly selected hams (but selected from messages from the same
time window, obviously). 

What's the best spam/ham proportion to go with on the current set of 
things to be tested? As close to the real proportions as possible? 
1:1? 2:1? 10:1?

Anthony