@kivexnz i I understand.
Though before going into the process to optimize your website for 5k retina ready display, If not yet done, I would definitely try understand who your target audience is. I had a client willing to optimize full width images for 4k retina displays but realised via Google Analytics that 80% of his user were requesting the website from mobile devices
Resolution of images really is a tricky question, but well since we can now lazyload images… by the way, why not use Webflow native Webflow srcset generation instead of the data-src attribute ? The data-src attibute will load the 2500px wide image on mobile too (heavy)… native srcset would load a more appropriate one.