The way I do it on my YZ250 is:
1. Start it and warm it up with minimal revving until the radiators are hot to the touch, then kill the engine. Let it cool for one hour.
2. Start it and warm it up once again, until the rads are hot to the touch, then ride it for 15 mins at 1/4 throttle; kill the engine. Let it cool for an hour.
3 Ride it for 15 mins at 1/2 throttle, kill the engine when done. Let it cool for an hour.
4. Ride it for 15 mins at 3/4 throttle, kill the engine when done. Let it cool for an hour.
5. Then finally, ride it for 15 mins WFO, or as much throttle as you can give it; kill the engine. Let it cool for an hour.

After all of this, I still ride it at about 1/2 throttle for a ride or two, and then it's ready to race.

I think after all that, it would be time to replace the piston and rings.

You're parroting numbers and you don't even know what they mean. You say the forged piston runs .0007-.0009 what (inches or mm?) Cast runs .005-.007. You say forged is 10x looser but your numbers say otherwise. I don't know about 125's but Wiseco specs .0015" for their piston to cylinder clearance in a 250. That is the same for cast pistons. Rings, forged or cast are identical. You can put OE rings on your Wiseco and Wiseco rings on your OE piston.

Ok, forged pistons dolike to run looser in the bore (vs. cast hypereutectic) and do take longer to warm up. That doesn't mean they take longer to break in. The fact is, you're not breaking in the piston, you're breaking in the rings.