I maintain several 9-speed (rear cassette) road bikes (Giant OCR 1/2/3, Tiagra and 105 from 2000-ish era) and one 10-speed rear cassette 105 road bike, made in 2007. I'm trying to find out if I can buy "one" chain to fit all these bikes and get good shifting results, thus only stock one kind of spare. I've read some people say yes, 10 speed chain works even better on their 9 speed setup, but it's all so context-specific. Instead of guessing, It'd be great if someone had information based on experience. I would like to focus on shifting/riding performance, and leave out the issue of possible variances in chain longevity.
1) Based on actual experience, do any of these specific 10-speed chains work well on a Shimano Tiagra 9-speed rear drivetrain? Well meaning shifts without issues, not "noisy" compared to 9 speed chain. KMC 10.93? SRAM PC-1031/PC-1071? Shimano CN-6701?
2) Are there other specific models of chains, that work well this way, based on actual experience? (For example, maybe there are chains marketed as 9-speed that are actually spec'd to the 10-speed specs, or other chain manufacturers I didn't include)