I don't think the Hot Rails and Super Distortion T are stacked humbuckers, I think they're just regular humbuckers that are made to fit in a single coil slot. They still sound like humbuckers, although a bit different than a full sized one. An actual stacked humbucker sounds almost exactly like a single coil, but without the noise, like what Yngwie uses.
Anyways, if you're looking for a humbucker sound in a single coil size, the Super Distortion T is AMAZING. Super beefy, fat, yet clear. It's an awesome pickup.