2500 rpm /2700 rpm = 0.925%
As Peter pointed out, the relation between RPM and thrust is not linear at all. If you disregard engine efficiency, propellor efficiency, parasite drag and a whole load of other minor factors, thrust is related to the third power of RPM. So in reality, at 2500 RPM, the engine will be producing less than 90% of its rated power.
But honestly, you really need to look in the "performance" section of the POH for the exact numbers. Because things like density altitude also have effects on the engine power output which might not be apparent from the RPM alone. (After all, if the air is less dense, it takes less power to spin the prop at 2700 RPM.)
If this is correct and I am calculating this the right way I wish I had bought myself a CS prop !!!
If your engine has less than about 200 HP and you're not too worried about extreme short field take-off performance, you'll find that a cruise-optimized fixed pitch prop is about as efficient as a CS prop, in the cruise. But fixed pitch props are less complicated in operation, and far less costly in maintenance/overhauls etc.