I just made a bundle (edit: no pun intended) buying up all borean leather (40s-60s each), converting them to heavy borean leather (which sells for ridiculous amounts now - about 6g each on my server, and selling them.

6 x borean leather = about 3g
1 x heavy borean leather = 6g (minus 5% AH cut)

Also, artic furs still sell for more than the price of 10 borean leather (which is the exchange rate), but the profit margin is a lot lower than borean -> heavy borean.

Depends on server economy of course, but might be worth checking out :-)