Using faster. more powerful motors than the stock nQX motors may result in higher speed flying, however the nQX flight controller does not work well with the additional power in certain circumstances. Quadcopters using the NQX Flight controller and faster spinning 6mm motors often exhibit a slight shimmy/wobble when hovering in stability mode.
Although frames designed to fit 7mm motors and accommodate the stock nQX flight controller are available, it should be noted that many builds using this particular combination can result in a very fast quad, but may exhibit a shimmy/wobble when hovering in stability mode. This symptom can be reduced by using slower spinning 7mm motors and the larger 120 frame, however it may still be present. Fortunately this condition does not appear to be present when using agility mode making higher powered options much more feasible if using this flight mode.
It should also be noted that with very light builds, even in agility mode the starting speed of some 7mm motors may cause the quad to climb as soon as the motors start to spin. A minimum battery size of 300mAh and motors no faster than 12000kV are typically recommended, however faster motors have been successfully used with heavier builds. Changing the battery connector is typically required when switching to larger size batteries.
Successful builds using the nQX flight controller with 8.5mm motors are possible, however slow speed motor options must be used. Flight times are also typically much shorter unless large batteries are used, so this is not typically recommended.