I'm not sure I really understand why you would want to do this, other than for cosmetic reasons. Replacing alloys is a waste of money unless you really don't like your current alloys.
Which Golf is it you drive?
To a purist like me, if you have Cadiz alloys on anything other than a Golf R, it will look wrong. My wife noticed me frowning at a car at the weekend and asked me what was wrong. I replied - that car is not an R. As we got closer I realised it was an R
LINE In our local seaside town at the weekend, I often find myself playing a game of 'what Golf is it really?' It amazes me the length some people will go to to make their cars look like a performance Golf.
If fuel economy is you main concern then driving mode and driving style will have a much bigger impact. Though if you have a GTI or Golf R then you really bought the wrong car. Thought for the performance they offer the fuel economy is reasonable. Even the GTD can be uneconomical in certain conditions - short journeys, sport mode, heavy right foot.