Canon 4000 series printer heads

Does anyone have any insight into the differences in the 4000, 4100,
4200, 4300 and 4400 print heads?
I have a 4400 that not long after purchase started printing vertical
lines at the end of each pass ( I think , ) as the head changes
dirrection. I happened to measure the voltage between the printer and
the computers ground ( because I noticed a tiny spark when connecting
the two ) and got around a volt difference. It could be normal or
possibly I got a ground loop and some transistor/driver blew.

In any case I was also wondering if the problem was not in the print
head. I have an opportunity right now to get either 4100 or 4300 real
cheep but not sure if the heads are compatible, although, around the
time I first received it ( gift ) I may have sean somewhere, print heads
for sale. At the time it was all new to me ( BC21,BC this or that) so I
am not antierly sure if it was a print head/ink cartridge holder or an
ink cartridge itself, if it was the print head then thy are most likely
all the same.

Maybe I could even buy say the 4300 and swap the ROMS to upgrade it to 4400?

Thanks for any help.
Sam.