So, nearly twice as fast to write with 8 bits, but whether or not that's important I guess depends on the application.
That is because of a 'feature' of the LiquidCrystal library that Bill mentioned in the previous post. The LiquidCrystal library includes an unnecessary delay between the transmission of the two nibbles in the 4-bit mode that almost doubles the time it takes to transmit a byte of data to the LCD. A library without this 'feature' would give you much closer times for the two modes of operation.
Don