Many thanks to all answers.

My conclusions are:

- stored procedures can have a result set with many fields,
where as UDFs are functions with one scaler as result, resulting in a different syntax
- stored functions are/will be availabel in FB 3.0

- I will code stored procedure always with suspend, to be more flexible and to use the more elegant syntax of 2.5 for returning scalars
- there is no remarkable performance drawback using selectable procedure versus executable procedures returning values
- I do not use "select *" as in the example, but always column name

- I keep on learning Firebird SQL.

Best regards
Christian Waldmann