Bf 110C issues

[Remo]

1. I had issue with all compasses (Gyro + Magnetic) stop (always display North) but mouse over does display a value ie the correct numeric value. Persisted over multiple missions , had to resart game to get compasses back.
2. The artificial horizon sometimes stop functioning.
3. Also the 500km/h (IAS) at any altitude is a big problem.

Regarding the performance.
I think the current model is quite forgiving on the side of the engine ( not by much but you can abuse the engine a bit more than the spec suggested you should )

Do you have the graph that maps the optimum climb speeds vs alt .
I'll try to match the climb times in your graph, but I think they are close upto about 4500 m , from there things start to go wrong.

Over 5000m the engines start to spit little dark smoke clouds and no longer run smooth (rev counter starts to oscillate between 2100-2400 rpm ), looks like the mixture is to rich. (no sound of backfire though)
On the oscillating rev counter , I'm not sure if that is quite correct , a real engine that oscillate rpms like that will probably break apart, and you have the heavy flywheel effect of the propeller, so even if rpms took a sharp drop , it should not be able to pick up 200-300 rpm in a fraction of a second.