Number Sequence Formatting

When using a format such as PO#####_XXX, I am told by MicroSoft that AX v.3 will accept this with no issues. However, MS says that v.4 has a technical change in the database and such a format will slow down performance. MS now recommends that the number sequence not use a prefix such as PO##### ... although the delivered product still has some number sequences with such prefixes. MS recommends that if a more easily identifiable number sequence is used then a suffix be used ... such as #####_PO2007, etc.