Are 45 degrees tracks recommended (I suppose they are slightly more space efficient) ?

Octagonal inductors have a higher Q than square ones, so for that reason alone I would want to be able to use 45 degree tracks. More generally in any situation where track length is undesirable (series resistance, capacitance etc.), you can save up to 30% i.e. (1-sqrt(0.5)) by going diagonally.