what is the safe rpm i can turn this motor?

Depends on what you have done to it:

Stock motor, govenor controlled- limitation is floating valves at about 4400RPM but each motor is a little different. On the Mikuni carb kits, the rev limiter kicks in at 4350 to keep you below that point.

If you have the valve springs shimmed (one of the common things done when people have head work completed) then the next limitation is the stock connecting and push rods at about 4600 RPM.

If you have a stock set up, set your govenor at about 4250 out of the water. Then go run your motor in the deep water lightly loaded and see where your max RPM is when trimmed for your best speed. Then set your govenor 200 RPM over that RPM to accomodate for increase in shallow water and you will be good.

If you are running up to 4250 in the water, you have a hot motor and there's some other things to do.

so 4125 is a relative safe set with a semi worn prop?

so 4125 is a relative safe set with a semi worn prop?

You are fine.