I have a 2014 mk3 2.0d estate 4x4. I travel from WGC Herts to Cromer Norfolk 240 miles round trip mix of motorway and fairly fast A roads every other weekend, also frequent 22 mile round trip up the A1. I am getting consistent 46 - 47 mpg on computer for both trip (averaged), since last fill (actual) and total MPG (actual) for 2k miles the car has done.
That is with lane 3 cruising not slowing anyone else down and keeping fairly close to 60mph on A roads. I will let you know how mileage improves once the engine has loosened up.
The MK3 Octavia has the Haldex 5 4x4 system which is much lighter than Mk2 Haldex 4 and H5 only drives front wheels until just as you need 4x4. It is the additional weight which has the biggest impact on consumption.