When are you getting the IO error? Was it just half way? I found leaving the layer break at Calculate worked best for me and from my searching on google i think that's one setting that doesn't really make a difference. As far as fixing the Error, it could be a number of things, For me all it took was starting the program and Pressing Ctrl-alt-del, going to processes and setting the priority for real time, i think you can set this in the write tab in IMGBURN settings also. Also make sure you started it as an Admin.
As far as the other settings you just need to play around, I've read its suggested to do 003 disks at x4 speed, but I've kept mine at 2.4 because im getting perfect burns. I did notice if i raise my buffer size up i get better burns. I've read that you should clear your OPC before each burn, but that hasn't been the case for me.. Basically take everything you read with a grain of salt and go with what works.