No, it has to do with what split and regex produce, not with what they get (behind the scenes, everything is a reference anyway). The regex only has to create a short new string, while the split (even if there's a split into 2 fields) has to create a large new string. And that's taking time.

So, if you have a gigantic string, and you only want the first, short field, a regex is the way to go. But usually you encounter short strings, and that's when split works better, despite itself using a regex. (But a much simpler regex, and it even might be that the case of " " is optimized itself too).

-- Abigail