The "goal" should be proficient. That's a guy playing at the top of his game. To have all of your players at proficient is very difficult to attain, but to have the 7 or 8 main players on your team with strong or above is not. I try to never have my important players' GS go under strong.
There is a marked difference between a player with respectable GS and a player with proficient GS. This can be seen in your players' ratings at the beginning of the season. As their GS improves you will see their ratings increase.
Once I scored a basket that still makes me laugh.