I was curious too, so I plugged a couple of numbers into this:
An interactive, model-based calculator of cycling power vs. speed

With the default parameters for rider weight, frontal area, etc., the difference between 150W and 144W is 18.53 mph - 18.24 mph = 0.29 mph. Not surprising you can't tell the difference. At 100W vs. 94W, it's 0.40 mph. Over a 25 mile ride, that amounts to about 2.5 minutes. That would matter in a race, but is seems pretty negligible under most other circumstances.