Different oils have different thermal properties. Some oils dont take heat away from components as well, some dont release it very well. Some oils run cooler than others. Along with these temp changes are viscosity changes which affects oil pressure.
SO choose your oil ideally by the ambient temp your in and the average oil temp.
Thicker oils do not need to be used on older engines.....and 127k isnt old.
Synthetic has better properties, its main benefit is far superior wear protection, better heat and viscoty index, no VI improvers, no polymers, no sludge build up and longer drain intervals.
And all this bullsh*t about magnatec, clinging to cylinder walls etc etc.....ALL ester based oils will cling to metal due to the polaric nature of the base stock, Castrol is just making a big deal out of it.