I am using Lightroom to prepare images that I will use in Muse slideshows--basic slideshow widget. In LR, I have cropped virtual copies of everything to the exact proportion I need in Muse. In the LR Export dialog, I use the Image Sizing dialog to set to my exact pixel dimensions for the images--784x560px, 72ppi. That's for my desktop version, but I'm using the same images for my tablet and phone versions. In the LR Export > File Setting dialog, I set JPG, sRGB.
My question is this: What is the optimal QUALITY setting in the LR Export > File Settings dialog to produce the smallest file size and maintain excellent image quality in Muse webpages? The QUALITY slider goes from 0 to 100. Furthermore, since my tablet and phone slideshows are smaller than the desktop slideshow, would I be wise to produce another set of images in LR for each of the three formats, sized for the respective formats?
Note that I am not using the HiDPI setting in Muse Site Properties > Content.