A 2.5% Gross gradient with 100 feet obstacle clearance is provided in PANS-OPS missed approach procedures.
Not quite. It's actually the minimum nett climb gradient. There is no allowance for performance degradation from gross to nett, so the aeroplane has to be able to achieve at least 2.5% all the way through the missed approach.
FullWings...
but where does this 2.5% gradient with 100' end?
It depends on how long the Intermediate Missed Approach segment has to be. If there's a lot of obstacles around then, yes, it might apply up to 10,000+, as you say. The Final Missed Approach segment only guarantees 164 feet of obstacle clearance, which isn't a lot more than 100 feet. In this country, however, if the obstacles have an elevation in excess of 5,000 feet, the MOC is multiplied by 1.5. If obstacle elevation is 10,000 or above, MOC is doubled.
I don't think this is done anywhere else in the world, but I could stand to be corrected.