Speed has no correlation to higher rankings. Although if your website is INSANELY slow, it will decrease your rankings. So, it is a factor, but at the same time, it isn't unless your site is of a horrific quality.
That being said, quicker sites will convert better, have better UX metrics, which in turn could indirectly help your SEO & profits. So I'd still losslessly compress your images, and scale them, yes.