Which wheel width on a Sprint?

[Dolomite16V]

Could anyone advise me as to what width of alloy wheel I should go for, as I am about to buy a replacement set for my Sprint and they are offered in 5.5 an 6'' widths. Is it best to stick to the original or will the 6'' give any benefits - both types of wheel are the original 13'' diameter, also will I need the 3/8'' or 7/16'' wheelnuts? The car is on an R plate. Any advice appreciated.<br>
A.Z.

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