I always render in bryce as a .tif file, and then save as an optimized jpeg in photoshop until it's around 150k I never go above 165k when posting in a public gallery. Often though, I will have renders that when saved as a 100% quality jpeg from a .tif are only 70kb in size!!! For most images the quality is usually around 70-80 for the best balance of file size versus image quality. Even at 60 quality the image loses little quality.