Useful info, thanks. The problem at this time of year is the weather, dark evenings and various family and work commitments; I will count myself lucky if I can fit in a 30-40 mile ride each of the next three weekends before I depart and ideally one of them a good 60 miler with 3000 - 4000 ft of climbing. A good ride leaves the leg muscles feeling tight and it's my belief that it is best to allow the muscles to recover completely but not to the point where they begin to lose tone, before stressing them again so my "training" consists of a weekend ride and a midweek mountain bike night ride or an hour on the turbo trainer where I give myself a hard workout, which I reckon is as good as a two hour mountain bike ride anyway.
In the last two years I have come out of Christmas and January feeling distinctly podgy around the waist and unfit having only done the occasional mountain bike trip. This year I have the heavier CX bike with mudguards as a winter trainer as well as a turbo with HRM so I'm feeling a lot fitter already. If that is enough to make me 6 minutes faster over the 68 miles, I'll be happy!