833 spacing
I was beginning to worry a bit that it was my age.
I now fly a CE680 across busy Europe and am quite horrified by the number of readbacks correcting the change of frequency. To a controller it must be very frustrating and time consuming. Having flown for some 40 odd years, it has never been so busy and so important that instructions are correctly adhered to.
However, I agree it could very many years before a solution could be agreed.