Well if you are going to run HV cyclics, a HV tail will simplify things and allow you to set the BEC at 8.4v and let those servos come to life.
I like the Savox SB-2272MG HV rudder servo, but there are many great HV tails. The Futaba BLS256HV is probably one of the best available if you can swing the price.
Just know that there is NOTHING wrong with your setup, just make sure you set BEC to 6v with the 1290 tail servo.