Nice choice! My first FA is similar to yours (plus micarta grips and a 3 lb trigger) and I've got a 7,5" octagon .454 on order. I thought about the second cylinder in .45 ACP for my gun also, but after studying a little decided to go without. After living with the gun for a while I'm in agreement with Mark; it's easier to just load down than to play around with the second cylinder. I, for one, am lazy when it comes to changing things with my loading press. As I load only 9mm and .454 at the moment, I only need to use small primers, SP for one and SR for the other of course.
I noticed that the softest loads shot a good bit higher at 25 meters, but some of my medium loads actually shot to the same POI/POA as my full house loadings. I've tried everything from mild to wild with my FA and I prefer to shoot from medium to high end loads, but not just because of the same (or in some cases close to same) POI. I feel that those loads really bring out the excellent ergonomics and potential that's built into these fine shooting machines...
I bet that you enjoy the very different loads you can shoot with your Casull; I know I have.