You're right about it being reminiscent of the dial-up area, but I don't believe it's 300 to 1200; it's more like 4800:

Modem vs Claude according to Claude:

300 @ 2368 characters - 1m 19s

1200 @ 2368 characters - 19.7s

2400 @ 2368 characters - 9.9s

14.4K @ 2368 characters - 1.6s

33.6K @ 2368 characters - 705 ms

56K @ 2368 characters - 447 ms

Claude @ 2368 characters - 7.9s