I run my f550 with the std dji motors with graupner 9x5 props.
If I were to upgrade the motors I would prob go for either the 800 KV or 900 KV motors with 10" props, this would achieve a little more efficiency and longer flight time.
Sunnysky motors are nice, I have the 900 kv's on my discovery.
Quadcopters.co.uk sell the torxpower motors, not a bad price too, ideal if you want peace of mind if any problems arise.
