Sometimes this is not very critical, other times it is what people are measuring performance by. Macs always run PCI at max. IDE can run at a fraction the speed of SCSI, and there are other issues. It seems that all devices on an IDE controller have to be running the same protocol. Some people buy another IDE controller to get around this problem.
Floppies are slow.
There are other gotcha's. And there are many things I did not mention like - Modems. The real world results are that the Mac flavor will usually blow the PC flavor away - but that is more the type of port chosen. The end results vary.