1.4 versus 1.8
Unless you really know what to do with your equipment, and what you need, you propably don´t need the last drop of it.
Faster lens - 1.4 - can make better background blurring and can make you shoot with faster times, but not so much, and not in every situation. It can be 25% advantage in certain situations, but it can also be ZERO advantage. Then, you have to decide, If you are likely to have longer end (more zoom) for Olympus, or not.
That what you are asking for is not as important as your comfort during handling and shooting. I´d go for XZ-1.
Why does he do it?