grant,
assuming your Primera had the same stock tire size as the US version G20... the stock tire size was 195/65/14 which has an overall diameter of 24.0 inches (not sure of the mm's)
for a 16" wheel.. 205/50/16 will give you the closest overall diameter to the 24.0 inches. 205/50/16's are usually 24.0 or 24.1 inches in diameter depending on the brand. this would give you zero or very little difference from stock.
205/45/16's will be undersized compared to stock, and will give a greater error as far as speedo calculations. 205/45/16's average around 23.3 inches in diameter