I am looking to pirchase a TS TG with 525’s, how fast will it be?

How much?

Found one for $125k with 260 hours.

there are sever factors that come into play in the top speed

84-87mph.

That’s a good price in this market depending on what’s what.

should run 85.

Assuming it is a 38' Top Gun with a standard side by side 525EFI & XR setup...
...83 when fully loaded up and
...87 light load, perfect conditions, propped correctly with a driver that knows how to squeeze out the last couple MPH.
IF the motors are not tired.

It's pretty much an 85mph boat.

I believe at 260hrs, most likely the top ends of the engines need to be redone. Factor that in your budget.

Fast enough that the insurance gods will likely hang up or tell you to quit talking and try somewhere else.

I'm more interested in where you found a 38 twin step GUN for $125K with 525's. Pix or it didn't happen! lol (kidding).