The earlier response gives you a good idea on how to correctly size the cable to work reliably and comply with standards. However there was another element to your question ant that was energy efficiency and payback which was not really addressed.
This is a question of whether to oversize cables or not. Any cable has an loss due to its resistance. The correct selection of cable will result is a given loss. If you then select a cable of larger cross section, the resistance will be lower and thus the loss lower. To answer your question, you need to calculate the resitance of the minimum cable which will do the job. From this and the load current you can calculate the loss in the cable. From the operating cycle of the load over time you can calculate the kWHr consumption and from the $/kWhr cost you pay for electricity you can calculate how much it will cost over a period of time.
Do exactly the same for the cable of the next size up or even two sizes up.
You can then compare the two and you will know how much the bigger cables save you in energy costs and you can compare this with the capital cost of the larger cable to see if it is a value for money proposition. You have all the info that you need to run various payback scenarios on which to make a decision.
When you upsize cables make sure that the equipment you are feeding can accommodate the larger cables as equipment these days is often very tightly sized. Check what the fault current will now be because the larger cable will give less resistance and thus higher fault current. The cable wiill most probably handle it but will all other equipment in the chain.
Another aspect as to whether to choose aluminium or copper cable. You will need larger cross section aluminium cables than copper to achieve the same losses but often aluminium, even in the larger size is cheaper. Remember though here it is not just the cable cost to consider. The terminations are also more expensive as you often need bimetalic lugs, you need to make sure that the equipment you have is able to accommodayte the larger cross section on its teminations and the aluminium cables will occupy more area on your ladders or in conduits. Some atmospheres are also injurious to aluminium but not copper.
Hope that this satifactorily addresses your question.