Mike,
First, if you need a different base punch, you do not have to buy an entire die just to get another base punch. I'm getting one more die, and 3 different base punches. The base punches for my particular set up, are $50 each, yours might be different, thus probably a different price, but nowhere near a price of a die. If you look on the Corbin site, and look up the style and kind of dies you have, you should be able to find the right base punch that you would need.
As far as BC is concerned, and going by your statement above, the shorter one of the same weight should have a better BC, just because there is less of it for the wind to take sideways. I really don't involve myself in BC's, other than looking for the best one that is accurate out of my Field and rigs.
Keep me posted, it'll be a few weeks before I get the rest of my equipment.
Tom Holland
Field Target Tech