4 is ok as well it just gives you a little more padding in case something goes wrong, like if something dies in the tank and you dont catch it for a while.
If you are keeping a reef tank you are smack dab in the middle of the desired parameters. The confusing thing about alkalinity is there are three ways to convert the readings meq/L dkh and ppm Here is a link that shows the ranges of alkalinity you need to be in
This link will give you an in depth understanding of alkalinity and carbonate hardness in your tanks good reading but a little intimidating if you flunked chemistry.
