Is there a rough rule of thumb to estimate what intensity will be achieved if we use the same parameters?

Ie we achieved 8 Almen A with shot type 230 that roughly equals X almen C ot X almen N

Yes. The standard guide is that "C strip reading x 3.5 = A strip reading and A strip reading x 3.0 = N strip reading".

10 years after creation of the topic, I have some questions about that famous conversion: C strip*3.5 = approx A
I never had any success with it, often it's often more close to something arround 4 for me.
Does it work well for you?
If it doesn't not work very well, what should I conclude? One of the two type ( A or C) was inadapted to the intensity?

Jean,
The conversion factor is for refence only. You are not permitted to use a different strip scale than what is called out on the engineering drawing.