I am experiencing some instabilities with my setup lately. Sometimes after running for ~15min the LCD shuts off, or the raspberry pi turns off etc. I have configured the DC Converter to provide ~5.1v. No I am wondering if this is too high and it is overheating what the max voltage the ATXRaspi can handle. Is rather advisable to keep the power supply at 5v?
5.1V should be OK.
What is more important is that you have good strong connections and good cabling/jumper wires that carry that power.