ARX-R V2 frame is the fastest 5″/6″ class quadcopter currently on the market. It is a beautiful piece of engineering that has been developed by Ryan at https://quadstardrones.com/
The kit provides an option to assemble a 6″ true X quadcopter or a hybrid 5″/6″.
Note: this frame has been purchased and was not provided for review. I am not affiliated to quadstardrones.