Yeah I think if I was doing lots of descending with the prospect of crappy weather I'd choose discs too mate.
I have ultegra 10 speed on my commuter and I agree the calipers have a spongy, disappointing feel to them. Fine for pancake flat London but I wouldn't back them on serious descents. Even with swisstop or koolstop pads which are generally recognised as being excellent. I think the newer 6800 calipers are better and the 105 (5800) ones are supposed to be very decent.
I've had dura ace 9000 on my best bike and they were awesome. Like razor sharp and super strong. I'd happily descend on them with full confidence, even with carbon rims they're fantastic. I then swapped them with the rest of the groupset for sram and they were only marginally better than ultegra 6700 which felt like a real step backwards. Plus, i didn't like the look of them on my bike, so I swapped them out for EE cycle works brakes. These are things of beauty and on par with the DA9000. The fact I'm a bit of a weight weenie may also play into this love affair somewhat...
I still maintain though that well set up caliper brakes are just as good as disc brakes in dry conditions. Good cable tension, good brake cables, good distance between pad and wheel, good brake surface, good wheel / pad combo. But in the wet I'm sure it's a different story.
I think I'm more put off by the way discs look and the marginal weight penalty than anything else but I never denied being a complete tart!