Ive had similar probs when the alternator intermittantly stops charging,it more so provocable in high gear high load situations.
A m8 has had a similar prob with his s2 with the alarm cutting the fuel pump every know and then,i suspect that could be a wiring fault somewhere.
Also check the main live down to the starter,make sure it hasnt rubbed through the sheathing and is not earthing out on the block or as it cross the gearbox.
As for overboost you will get full cut if theres too high a pressure and or the inlet temp is too high.