Today I booked a C flight FRA-SGN rt. for me and my wife on the last day of the recent promos (multiple Qmiles and partner discount). I managed to get promo business (R-class) fares for 3.948,-- Euros for the 2 tickets. This included the 5% discount for partner bookings. I also tried to use the "mystery code" but it didn't change the price.
Whilst this price is nothing to write home about the Qmiles multiples made it acceptable. My wife with no status will receive 5x and myself as a Plat 3x. With my Plat bonus this adds up to 144.000 Qmiles which is quite nice.