One heat code number colder, so probably not a big difference. According to NGK the higher code number is a colder running plug, so better for more sportier driving or long hot drives I believe.
The lower number is a hotter plug i.e. it has a more projected nose (insulator) so the plug will get hotter quicker on shorter journeys or colder climates, this allows the plug to "self clean" better.
You could try running for 500 miles or so and then inspecting a plug, there will probably be a picture on the internet showing plugs in different conditions.
In the old days if we were running car that burnt oil and fouled plugs we would put extended nose plugs in to self clean and burn the carbon off, often just on the one cylinder that was oiling up.