Thanks to get back on this.
You right, the best way is to test and see.The reason why i asked is because the information online is confusing.
Some say don't even bother, some say it's based on cpu and some info like this is on sql server performance site so go figure
“This parameter tells SQL Server the number of bulk copy operations that it can perform in parallel. By default, this is set to 1. By increasing this value, bulk copy operations will run faster, and the initial snapshot will be performed faster.
As a rule of thumb, try a value equal to the number of articles you are publishing. Only one thread will be assigned per article, so there is no benefit of using a value that exceeds the number of articles you are publishing. You may want to experiment with different values to see which one works best for your particular configuration. If you set this value too high, performance might actually decrease because SQL Server will have to spend extra time managing the extra threads, outweighing any benefits provided by the extra threads.”