That sounds like a good possibility on the dual coils and their optimization for single coil use. Since the big singles have more of a wind, they would be a lot stronger than the DC's split to single. Definitely explains why they might be a little thin sounding. Not that I don't like them, but they are definitely more polite than I thought they would be when split to single.
Here is what Stew wrote me, comparing some of the pickups:
BigRigs, Big Singles, Big Splits and Fat Stacks have as many similarities as they have differences so I’ll try to sum up.
The Big Singles are Carey’s take on the ultimate J pickup. They use the same magnet load as a J, but the wind and rotated poles draw a lot more information from the vibrating string than a standard single coil J. These are probably the reigning favorite pickup here at the shop.
Big Splits were originally designed to be the hum canceling version of the Big Singles, but because during development and the way the coils are split they have developed their own voice. Where the Big Single is definitely a J variant, the Split has some elements of the P infused. It’s very full and very smooth, so it’s become one of our favorite pickups to recommend for a fretless.
Fat Stacks are really two pickups in one, but the design is not without its compromises. In single coil mode they have some some of what the Big Singles bring but they have a very nice low mid growl. The hum canceling mode has a bit less output (about 3dB) than single coil function with a tone that’s darker, warmer, slightly mid scooped and overall more polite.
The BigRig has been a really exciting development and while it has the organic and dynamic qualities people associate with Nordstrand, its voice is all its own. It doesn’t sound like anything else to my ear and I describe it as the most elegant sounding thing we make. The coils are derived from the Tele-style P, but other than their fullness you won’t really hear the qualities people generally associate with that design. They are gloriously articulate and cover a lot of ground sonically. These are fast becoming a shop favorite. I think if you’re looking for something different you will be more than pleased with the BigRig p-ups. They really are just elegant.
I sent Stew a question today as far as size options with the pickups, but I've pretty much decided those are what I am going with. Of course, now I have to wait 6-8 months for the build to be done to hear what they are capable of!