During the winter I use one of the lower weight lubes and I clean & lube the chain after every ride home (I also use an old toothbrush to lube the cog each time). It helps prevent rust and I'm guessing it helps keep the slush from accumulating because the lube keeps the snow from building up on the chain and there is less of it for the chain to transfer elsewhere. Lubing the cog may also make it more "slick" so the slush doesn't stick to it. Some of the other cheeseheads use a heavy weight lube so they don't have to clean & lube each day, and perhaps that helps with the slush because I've never heard them complain about it.

Temperature does play a part no matter the type of lube, because if it gets cold enough the water & slush will freeze to parts of the chain, derailleur, and pretty much everything around it. When that happens it doesn't fall off as easily or as quickly as it would in other conditions. I learned this on a 2 hour beach ride when it was 14 degrees with a 10 MPH wind. Towards the end of the ride the bike was shifting bad and making sounds and I thought something had broken, but it was just the chain hitting all of the ice surrounding the drivetrain and the ice build-up in areas close to the chain was affecting the chain's movement.