For me I was happy with sending 5, and I always send a lil extra something, whether it's a fq or a fq and a few charms, or whatever. I don't expect to get anything extra, though
4 seems like not enough, and in terms of postage, I don't notice it's any cheaper to send 4 rather than 5, as it goes in increments of ounces to mail 1st class mail. If it is any cheaper to send 4 instead of 5, it's less than 20-25¢ cheaper.
And for those who use flat rate envelopes, a lot more than 5 fqs will fit, so postage isn't even an issue on those.
I'm happy with whatever the group consensus is, though
Regards,
Kif