I am developing some software for the Commodore 64, and my intention is to use the 1541 as a coprocessor. I'll have the 1541 compute some data for me, and then retrieve this data over the serial line.

I know that the KERNAL routines have earned themselves a reputation for being very slow. I couldn't find any information about exactly how slow though! So what I want as some concept of the relationship between the transfer of X bytes, and knowing how much raster time approximately needs to elapse to transfer this amount of data.

Unless I rethink my design, I will need to transfer a payload of around 40 bytes per frame. If I use the KERNAL routines, what kinds of speeds can I anticipate?