What is the impact of changing to a smaller chainring?
I would consider changing your crankset to a true compact, 50t/34t, and running an 11/25 rear cassette. 

Campy actually made a specific derailleur for running a compact front, because they said that the 50t doesn't work well with the standard front derailleur (that may be a function of the tooth differential, so it may not apply if you leave the 39t in place). 

(Edit: It does appear that my data on the campy front derailleur may be outdated. Their 10 speed Chorus and Record had an individualized front derailleur, but current product appears more universal.)

The 50t x 11t combo is a 119.6in gear, compared to 107.2inches for the 53t x 13t you're running now. 

It will give you a slightly faster gear than current, a better climbing range, and slightly crisper shifting. Downside is you have to buy the crank set and cassette, not just a chain ring.

Check out UBI gearcalculator for more info on how gearing changes will affect you.

Hope that helps.