I am only going to say this once!
As everyone knows raising the pressure on a liquid increase its boiling point, that is the main purpose of a pressurized cooling system.
The thing with the E46 the cooling system uses an expansion tank so the coolant is pressurized against an air pocket long before it even gets close to the 2 bar pressure cap.
The pressure release in any cap is more of a safety valve or mechanism, just look at any water heater pressure release valve.
1 Bar is approximately 15 psi, which is about where most domestic cars run that do not use an expansion tank system.
2 Bar is approximately 30 psi, which is totally absurd for any car using an expansion tank system.
Just look at all the expansion tanks that burst the minute new BMW owners check their coolant and top off the expansion tank like it is a domestic car with a radiator. This is when the pressure cap is pushed towards its limit and just looks what happens, BOOM. There is no way most of the parts in the E46 cooling system could survive 2 Bar on a daily basis. Also I would hate to have the heater core blow under 2 Bar and dump scalding hot water on the occupants feet.
You can also squeeze the upper radiator hose on the car and feel there is nowhere close to 2 Bar of pressure in the cooling system, matter of fact there is probably nowhere close to 1 Bar in the cooling system under most situations. Almost anytime the pressure cap is removed from the expansion tank there is very little pressure built up.
So until someone has connected up a pressure tester and logged the cooling system pressure under daily and track conditions and can prove these engines even get close to 1 BAR, I think all this concern over not using a 2 Bar cap is a waste of air and mental capacity, assuming there is much mental capacity to even waste!