WILDWOOD DESIGNS! Unsure if they are on houzz but in gladesville and do amazing big tables.

Like the previous comments it depends on use and the design of the light fitting itself. Also if the light has a narrow beam it may need to sit higher to throw a wider beam to light up the area you need lit up. Generally you would put it above eye level so that it doesn't obscure your view when standing. More often than not it is just a matter of where you think it looks best, most pendant lights have good adjustment so before its installed have the electrician hold it up for you at different heights and see what looks best.

It might be worth while to consider the rest of the space also. Your breakfast bar/kitchen is located quiet closely to your dining table so depending on your kitchen space (apologies, I can't see too much of your kitchen from the photo) you might want to think about the overall style you want to achieve for you entire open plan space, and select pendants that would work for both your kitchen and dining. This is a project I worked on recently that shows how two different types of pendants can work harmoniously in the one space that is most similar to your kitchen and dining set up. Keep us posted on what you decide!

@oklouise Thank you so much. The measurement above shall be an accrurate one ( I measured myself not long ago :) But sadly we are in the middle of reno already. Walls knocked off and plan is as per I shared with you. We are struggle on the dinning / living area while we scratch our head where to put our TV but at the sametime the dinning table location makes sense.