I love my 4. It's small enough to easily carry, but still has the blade length to do a decent job at batoning wood. It's also very well balanced and is comfortable to use. I paired mine up with an Izula II and now my addiction is becoming worse because I want a 6.
Pairing up the 4 with an Izula II is a great pair....really pairing up an Izula with a 4 or higher is a great combination!
I haven't received my 6, but I think my Izula II, 3 or 4 (serrated?), and 6 will make a great team.