You mentioned the Bullnose. I have the Super, Combat, Bullnose, and La Griffe, and frankly I find the applications for the Bullnose to be kind of limited! For knife boxing, the only place I would choose it would be held blade forward for crossing punches.
In reality, the Bullnose is just a short CQC-10. I know those who are use to classical straight bladed knives, will probably be attracted to the Bullnose just because it resembles something they are use to.
It is worth getting Emerson's traning DVD's, especially if you can't imagine all the different ways you could use a Karambit. Used in knife boxing, you are going to pary and block your opponents moves, yet instead of a bare hand you have these exemely wicked blades at the end of each fist! You opponent is likely to quickly decide that the cost of getting sliced and diced every time he moves, isn't worth it......
Right now, I am carrying the Combat Karambit on the strong-side, and the La Griffe on the off-side (La Griffe techniques are just like Karambit techniques). If I were in a very high risk environment, I would go for a two Combat Karambit carry (one waved forward, and one waved backward).
I have found the Super to be a little large and a bit clumsy for boxing, but a longer blade is sometimes nice. As for the Bullnose, sometimes you have to buy something and try it out, to know how it will actually work in the real world.