Secret Santa,
sorry i should of been clearer - oil for me in curry is always reclaimed from the base not fresh veg oil.
saying that - i've heated reclaimed oil, veg ghee and butter separately as part of my garlic frying trials. the butter and reclaimed oil seem to be more tolerant in after taste than v.ghee - the v.ghee after heating to smoking point seems to have a "processed" after taste. butter has a lower burn point and even easier to spoil the taste of.
the only place for v.ghee for me is in the base.
butter ghee - i've not tried for a long time - the taste is too overpowering for me.
i suspect that a mix is used in "v.ghee" BIR's. i also know some BIR's only use oil from the top of the gravy.