The Type-6 is probably the tipping point from making more money on trade runs then rares. The Cobra on the other hand is pretty well suited to trading rares (reasonable cargo hold plus good range).
Managed to get my Clipper. Took a while getting the ranks and a couple of goes taking down a Clipper in my Viper (bloody rammed me the first time...) for one of the ranks. The size of it has meant a couple of problems; can't dock at outposts and I now have to wait for NPC traffic when undocking. Unless it was large ship, I was always able to squeeze the T-6 through!
I guess I'll start trading in Fed space to start working on their ranks.