If you scroll down the page on dsscircuits.com you'll find a pretty detailed timing comparison between the I2C and wire library ;-)
That should explain any performance differences.
It does - in favor of the Wire lib. Compare bytes/us or us/byte. You'll see the Wire library is faster (more bytes/us or less us/byte) in all three cases. However, the text says the results are out of date. Note that the interrupt code may not have been removed in that version of the library.
However, micro-controllers are about real-time events and polling tends to block the real-time system. Or does it?