Hi Vlad,
Sorry, missed your reply here.
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Using the ‘shared assets and resources’ to host the fonts (.eot, .ttf…) via cloudfront, rather that the default uploader location on AWS, it seems to be a tad faster. However I unfortunately didn’t do a test prior to the switch over as to what the actual numbers are before and after. I guess this probably depends on the number of custom fonts being used, for less than 2, probably nothing to impressive, but more and its probably worth it.
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So yes, when I can, I’ll use the modifier to process with imgix to set the quality of an image (usually for me about 80% is fine and doesn’t comprise quality) along with using the ‘auto enhance’ feature to get the brightness levels up at bit. However with static and dynamic images, I’ll compress them locally before uploading them to either the in-element image or into the database to call from a ‘do a search for’. I use some free software Caesium (https://saerasoft.com/caesium/) which I’ve found does a good job at re-sizing and compressing with very minimal loss and shrinking kb or mb right down. Most of the images I’m talking about here are background images at large dimensions, this is where the file size can vary e.g. full viewport backgrounds. Probably for small sidebar graphics its not worth compressing locally, imgix should do the job. But say a large slideshow of half a dozen images, I feel its worth it.
I regret not doing some tests before and after the changes mentioned above, I feel like pages that were impacted run a bit faster, sure nothing game changing, but every little helps right 
I’m tempted to run a few test with the fonts, as before it was noticeable on the network timings (3 custom fonts at around 700ms load time each). Also a quick test with some background images and the page load times with fresh cache would be worth some testing to evaluate if there really is a decent speed increase and if its worth the trouble…