The 6.0v thing comes not from the gyro capability, its the servo supply on helis where the tail servo never stops moving and overheats on 6v+. A 4 cell Ni pack is just under 6v in operation, but a 5 cell (6v) pack is NOT 6v its 7volts ish and the servos overheat.
Some gyros have both modes, but Digital servos are perfect for gyro use.

Dw