I did quite a lot of medium distance rides (50-80 miles) with plenty of hills thrown in, last Winter. In particular I had a pretty good January, in terms of mileage clocked. I think it helped a little, as this year I have been generally stronger and faster than last year (even though I am 5-10Kg heavier).
I took the steel hack with it creaky headset and full guards on one club run a few weeks back. Blowing out of my *rse to keep up with the fast group, so I have been on the alu bike and sticking with it for all but the wet commutes. The Supersix is clean and sparkly and staying put in my bedroom until Easter eggs become available at the shops!
There's a Winter series on a closed circuit, that I am considering. Hoping it might motivate me to drop some of those nasty extra Kg's...
Was thiking about CX too but they cancelled Muddy Hell and that was the one I had thought about trying.