I'd do 56kbps download, 48kps upload, at 100ms. Still loads this comments page fairly fast!
Kilobits or kilobytes? A 56k modem is max 56 kilobits/s, a.ka. 7 kilobytes/s (although realistically I never synced over 50k, and more common something like 48k)
The once popular developer site 15seconds was named because that's roughly how long a person would wait for a site to load... I'd say closer to 3-4 now is where I get really cranky.
I think it could be workable if you were to set uBlock to block all images and scripts.