Sir ungas mahal nga po ang synthetic compared to mineral oils. What made them more expensive is that they are being synthesized from scratch with similar molecules and better characteristics than mineral oils. Hindi po sila prone to breakdown that will cause sludge formation, higher oil viscosity and poor oil flow. Kaya po pwede sila for extended drain. Some oils with ACEA E5 classification could even go longer than 20k kms basta po minomonitor ang components ng oil like the TBN, etc... Medyo mahal nga po ang oil for a 5k km change kaya po pwede ding every 10k basta palit filter every 5k. Ganito po advice sa akin ng Mitsu casa with the use of their Mitsu Turbo XP !5W-50 synthetic. By the way the Mobil elvac MX is a mineral oil.