Well it depends on your ability. But I run an 8.5t Orion (equivalent to some low end 7.5t motors) and then add a bit of turbo on the Esc for straight line speed.
The Orion is lovely and smooth when you get the settings nicely balanced.
Try dropping down and see how you get on. It's improved thing for me.
Also I wouldn't alter the throttle curve as you loose the linear feel of the control