In 2006 I set my wife's bike up with new Campy 10 speed shifters and new 10 Campy RD with a Shimano 9 speed cassette. She has been happy with it for thousands of miles. Works well but not perfect. No problems with 10 speed chain, but the wider 9 speed chain makes some noise.
Converting a 10 speed cassette to 9 speed spacing is a good idea if you have a wider 11 speed hub.
Seems easiest to me to use 10 speed campy shifters and SRAM 10 RD with Shimano 10 speed cassette. Works well without duplicating manufacturers.
