Internet programming for the C64/C64u

I recently got my hands on a C64 Ultimate, and one of the great things about it is the built-in wifi. A great opportunity to do some basic programming that makes use of being "online".

In the past my internetty code for the c64 was using the serial modem, which is speed restricted, but the C64u emulates the Swiftlink cart and that can do 38400 baud which is considerably quicker.

Strangely, though, the Vice emulator seems to struggle with higher speeds and I can't figure out why ...