Thank you Mark for your answer.
I agree with you that the isonic 131 cross over the isonic 122.
But I don't like use the 9,4m on my IS 122 ( better suitable for my 8,5 and 7,6 m ).
The Isonic 150 what you say feels big and with a big fin it feels like a mini formula ( wath I don't like )
And I'm not so heavy as you are ( I'm 87 kg ).
So perhaps the Isonic 131 is still a good solution for my problem.
Selling the isonic 122 is not an option ( I lose too much money ) .