If you run a double 8 speed chainset and front derailer you may get slower shifts to the small ring. 8 speed chains are a bit wider than 9 speed chains so the space between the two chainrings are a little wider. When you get it adjusted so that the derailer doesn't drop the chain off the smaller ring in a downshift, the chain _may_ sometimes ride on top of the smaller ring's teeth before settling fully onto the ring.
You can adjust the low limit out further for faster shifts but you'd need to use a third-eye chain watcher to keep the chain from dropping off the ring.
I know this because I ran 9 speed Ultegra on 8 speed RX100 cranks and FD for a while before I got an awesome deal on Dura-Ace cranks.