[XJeepers]

Whilst you are lowering the boiling point by a few degrees, you are also lowering running temps few degrees as well.

30/70 = 105 degrees boiling point
50/50 = 107 degrees boiling point

This is unpressurised, so the 16psi in the sytem will raise this a few more degrees in both instances by 5 degress (IIRC). I don't know about the diesel, but that is redline on the petrol. Something else is wrong if you are hitting the redline on the temp (in any vehicle) in my experience.

When I was running 50/50, my system would often go just past 100 degrees.

Running 30/70, the first thing I noticed was that the system was running only a couple of degrees cooler, but the big thing I noticed was it spent less time at the 100 degree point. I didn't expect this last point, but it stands to reason that if the system has more water, it will be more efficient in sheding the heat.

Either mix is good in my opinion. I just think (at the moment anyway) that 30/70 in a healthy system seems to work well in my experience.