A couple of years ago when I built up my CX bike, I went 10-speed in order to repurpose some first gen Sram Red shifters I had in a bin. And since people were getting rid of their 10-speed wheelsets, I picked up a few spares for a song. When I built up a bike for my son, it was natural to use 10-speed so we could swap wheels whenever. Found a Tiagra mini-group online for a very reasonable price. All in all, it's a great bang for the buck.