In reply to Herdwickmatt:
At about 15 miles of gravel and 15 miles of road every day you are going to eat drive trains. 11 speed 105 double, with disc brakes would be my choice. If you've got much traffic on the road sections (ie stop start with traffic lights) then you will destroy rims with rim braking. If it's flat, you'd be better off with a fixie with that mix. I used to ride a mountain bike on that sort of ride and just left a fine trail of metal filings behind me, so I swapped to a fixie which just kept on running.
More recently, my ride has been all road and that sort of distance - on a road bike, but in all weathers. Every rotating component except for the rims, little ring and the cranks have been replaced (including the discs and pedals). The front derailleur is original.
For daily commuting over that distance you really need something that has attachments for a baling machine, a plough and a seed drill. I work on about £1/day in the kitty for maintenance/replacement. Two spare tubes and a mini-fumpa pump - because there's nothing worse than changing a tough commuting tyre in the pissing rain, pinching a tube and watching the CO2 disappear in a puff. Or running through a patch of broken glass and getting two at the same time.