VB Quote: "I am almost sure that the lost of power with 5% will be too much for this application."
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You probably won't even notice the difference in performance in the air.
If there is any drop in power, it will be slight.
If you have a good tach, you will see some difference, but in the air you won't see much difference.
The OS 1.20 is flown in many countries where nitro is not available (banned for illogical reasons).
So the engine will run OK on FAI fuel which is zero percent nitro.
But the engine will start and idle better with 5%.

The OS 1.20 on 5% will provide all the power needed for a Venus II.
You probably won't fly at full-throttle most of the time.
Regards
JC