the 56 will almost double your performance, definitely wait if you can for a month.
This is the option I took, decided to grab a Vega56. It arrived today!
It is installed in the machine but isn't working. Onboard graphics is active and nothing in device manager. When I had this problem with the RX480 it was a case of a BIOS update but there doesn't seem to be anything newer for my aging Z68A-GD55 (G3), currently on BIOS 25.8 (LINK).
Any other recommendations?