In your case I guess it doesn't matter. I assume that is with your ambient temp being about 22c. It's fair to assume if your ambient went up to 32c that your CPU would then be 70c. That's what normally happens when air temp enters cooler has a 10c temp increase. You probably have AC so will never be 32c anyway.
Doesn't change the fact that coolers able to cool 300 watts at same noise level as a cooler able to cool only 200 watts at same noise level will run quieter cooling 200w of heat. The 300w cooler will also remain at lower noise levels cooling 200w with filters getting dirty (restricting airflow), hot summer days, etc.
What Bencher said.
Having 300w of cooling ability on a 150w CPU isn't just for cooling in normal conditions, but also for keeping system quiet when rendering graphics in hot summer weather with dirty filters, etc.