Well, where to start. I like the Super 12 for "clean" area's, it gets a little better depth than the DD coil, even though I have bad ground where I am at (DC Phase at -93 to -95) the problem is, there are very few clean sites. The 10x14 is excellent at weaving between the trash, while still getting a respectable amount of depth.
The 10x14 seems to go about 10 to 11 inches on a quarter, while the super 12 in the right enviroment will get an inch or two better. Again, if there is any trash under any part of the super 12 it really hurts it's depth on the good target.
I am not a big fan of V.C.O pinpointing, but it is a MUST for both the super 12 and the 10x14. My stock coil will pinpoint very well without using V.C.O (but not quite as well as my 9.5 coil on my Eagle Spectrum) I have the "older style" 9.5 for my DFX. From what I hear, the "newer style" does not work as well as the old one (which are you using?)
I found there is little to no volume change on the super 12 once the target gets into the middle of the coil. That is a problem, since the center hole is so large. But I have found by using the V.C.O it pinpoints fairly tight and I am quite satisfied with it.
As for the 10x14, trying to pinpoint off the toe or heal is a nightmare. If you use the V.C.O it is very accurate at pinpointing just in front of where the shaft mounts to the coil. But it is cruitial to "X" the target with pinpointing with the DD or you can miss the target my more than a couple inches!
So I suppose in a round about way, you are asking which coil is right for you. Well, they both have there advantages. You said your ground was good to moderate, that would be a plus for the Super 12. You are hunting for civil war relics. How deep in your average target. If it is fairly deep, over 8 inches, another plus for the Super 12. Are the areas you are hunting "clean" or is there a good amount of trash? If it is clean, again the Super 12 wins. But if there is trash, take 2 points away from the Super 12. If the targets are, on average, within 8 inches and you want to cover 2 times more ground and there is moderate amounts of trash, the 10x14 would be better.
As far as how far can the detect an aluminum can, the 14-16 inch range on a larger target like that for either coil, but I presume if you have good ground, you can get another 2 or so inches on top of that. It doesn't sound like much, but when was the last time you dug 15 inches down. That's a long way down, especially to find a can. Also, if you are in "all metal" you will be able to go a little deeper yet.
The biggest problem I see you will have with either coil is they both seem to lose a little sensativity to nickels. I'm not sure why, but a friend of mine used the Excelerater 10x14 on his Minelad Explorer SE and he can find nickels left and right.
I will say this, if you are hunting mini balls, and they are within 7 inches, I highly recommend the Excelerator 4.5x7 coil. This little coil is really impressive on depth, seperation and sensativity to nickels, which falls in the range of mini balls.
The best I can say is, buy them both, you will need the one you don't have at least once!