Personally I've never found wet conditions to be particularly hazardous because the reduced speed and visibility simply don't give many opportunities for hard cornering.
I ride exclusively on well paved (but not necessarily well maintained...huge potholes
) roads and every time I've lost traction it's been due to either:
1. Sleet.
2. Dry sand/gravel...particularly this time of year as the melting snow leaves behind pieces of road dug up by the plows along with the sand they sprinkle over the ice.
I also detest a tire that's difficult to get on/off the rim (flats are inconvenient enough as is) and I much prefer a tire at least 1.5" wide to safely ride over big cracks (not all the holes are shaped like pots).
I recently tried the Intense brand Micro Knobby (also MK2) tire:
and liked them so much that I stocked up on 5 of them (on sale $10 each).
They're fast, light, cheap, and available in a variety of widths (according to Sheldon Brown, BMXers have a few things to teach roadies about tire width and traction...maybe you just need a wider front tire). The folding beads are also easy to get on/off rims without tools and flat resistance actually seems pretty good (with a couple hundred flat-free miles in wet conditions without a tire liner...IME most tires flat within 10 miles under such conditions). Don't let the knob pattern deceive you...it's so fine that they're really more like slicks with a checkerboard tread pattern than actual knobby tires.
One thing I can't speak about yet is the wear resistance...which I'm surprised the OP didn't mention as a requirement for "long distance riding". But at $10 each I'd still be happy with the Micro Knobbys even if they only lasted a season.
Schwalbes are also excellent (albeit expensive) and the Panaracer MiniTS look good (although I'm not much interested in the Primo Comets because the wire beads are heavier and more difficult for changing = lose/lose), but I've become somewhat disillusioned with the "slicker is always better" for road riding philosophy. I mean, in theory, sure a slick tire offers the most traction on a smooth road, but in the real world I think loss of traction is usually caused by a breakdown of that theoretical ideal than actual rubber slipping...but I guess if the PBP committee has carefully selected well groomed routes for you to ride on then you might not have to worry about it.