What is the difference in performance is on average? We should probably be calculating both of these options, with another ratio factor. The client should decide which method to use. This could become important when scaling up, if there is a lot of available work from different pubkeys.
I have no idea what the difference in performance is, as I don't think anyone has implemented the other method yet. However, I'm afraid it might be dependant on the amount of keys to check. I will add the columns in.