Hi,
Its not that small a change...the size of each image will quadruple from around 10kb to 40kb. As there are three images thats 90kb more data. Which is around 20% of the total page size.
That's interesting what you mention about the first byte load time. I would have thought that was overly simple and would definitely have assumed Google would actually be more concerned with how long it takes for the page "to load" (e.g. using their pagespeed metrics).
I've optimized my site extensively and have pagespeed score of 95% and I use the amazon AWS servers.
I agree with your idea about doing what's right for my users. But if Google includes the image load time then my site will rank poorly and then I won't have any users!
In summary, I think what this question really comes down to is how does Google calculate page load times and does this include image load time and does it include load time for all images (even ones which aren't being rendered in the slider).
Thanks,
Dwayne