Effect of Bicycle Chain Wear on Shifting Speed

Apparently, shifting times differences measured with new and worn "10 speed" chains are marginally low to allow for any statistically significant conclusions. So I guess the message is don't fret unnecessarily over your chain length.

Links to the two studies courtesy of Wipperman are : Test on new chains, Test on worn chains.

Two plots from upshifting and downshifting tests are shown below.

Speaking of chain wear, Wipperman's most conclusive test results on chain wear ranks themselves as number 1 in the list of 10 speed chains, which they attribute to their solid, no frills side plate and solid pins. Link.