I agree with you. It should take the same time when thinking more about it. I remember learning this in ~2016 and I did performance test on Skylake which confirmed (Windows VS2015). I think I remember that i only tested with addsd/addss. Definitely not x87. But as always, if the result can not be reproduced... I stand corrected until then.
I tried to reproduce it on Ivybridge (Windows VS20122) and failed (mulss and muldd) [0]. single and double precision takes the same time. I also found a behavior where the first batch of iterations takes more time regardless of precision. It is possible that this tricked me last time.
