If you are asking my opinion then I say keep it the same but I would personnaly not go any more than 5mm different. this will have an effect of changing the vehicle track by 10mm, though not really noticable in normal driving but has a difference when giving it some berries on the twisties.

So maximum you say 56 and minimum 46 roughly and keep the 7.5J
 
Spacers are also available to adjust the offset if the wheels you fancy are not a perfect match. Rather buy wheels that match, but it widens the options.

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