I have 3/8" line installed on my Catalina 22. CatalinaDirect is suggesting 1/4" for both my halyards. Will I regret stepping down to 1/4"; will I notice a difference?
Yes, you'll notice a huge difference. Could rven cut your hands. Party of line size is called "hand" which means how comfortable it is to, uhm, handle it, regardless of the material it's made of. Once it gets reallly thin, especially if it needs some oomph to pull on it, it gets tedious using thin line. If you can, got into a store with line, even a hardware store will do, and feel the different sizes, pull hard on them, too. Then decide if that's what YOU want to do. Good luck. I've found, regardless of boat size, and I've had a C22, C25 and our C34, that 3/8" is as small as I'd want to use, anywhere (except for maybe a spinnaker sheet for light air).