ok guys, here's the results for new tests.
This one is with SMARTBURN enabled which limits writing to 16x on these media, Overburned to 707MB with mixed data (703MB capacity)
This one is at 40x with SMARTBURN off not overburned, 702MB mixed data burned.
is this better?
I have no idea what im supposed to look at for c1/c2 errors etc! but from this I can gather that SMARTBURN does indeed help when overburning or it's the lower writing speed on the media but at 40x NOT overburned the cd is also fine