This depends largely on your operations. There is lots of performance critical code that doesn't vectorize smoothly, and for those operations, 64 bit is just as fast.

Yes, if you're not FP ALU limited (which is likely the case if not vectorized), or data cache/bandwidth/thermally limited from the increased cost of fp64, then it doesn't matter - but as I said that's true for every performance aspect that "doesn't matter".

That doesn't mean that there are no situations where it does matter today - which is what I feel is implied by calling it "Ancient".