Hi gabriel !
The best oil would be a 05-50 like mobil one or Esso Ultron, there is no better oil for your car ! a 20-50 would have been enough for somebody living in california but in belgium (
) were temperatures can go way below zero in winter, a 05-50 is surely needed in order to keep the engine going for many more years.
just keep in mind that once you have changed your oil for that kind of synthetic "super"oil, you must stick with synthetic oil for the future, coming back to mineral cheap oil would be bad for the engine.
Take it easy man !
ps : i am from belgium too ! close to Nivelles (Nijvel).