I built a 24" SS upper for AR15 based on the .204 Ruger cartridge, I love it, it is my favorite by far. My 17 is second.
I love going to the rock quarry and shooting the rocks off the walls at 200yds, they seem to vaporize with it, I have not shot any paper yet
but I am guessing it will be very good. Factory cartridges are fairly pricey at about $17/20 so handloading will make a huge difference.
besides then you can squeeze out more accuracy. I cannot however duplicate the factory speed. Although I can get over 4000 fps.
My next purchase will be a chronograph so I can be certain of speed and consistency. Oh and electronic scales for reloading.
I don't think I can tell any difference sound wise compared to the .223 but the cross hairs don't move much, followups are very quick.