We have a policy of no tankering if the landing runway is expected to be contaminated or if icing conditions are forecast for the approach. So regardless of length wouldn't do it. Remember that landing heavier than you need to for economic reasons is fine if you're not impacting safety margins. We also have to take into account next leg so as not to arrive with too much fuel. Imagine the next sector is very short to a short runway with a full traffic load. You may end up limiting yourself due to the next landing weight if you arrive with too much fuel.