Yes, the glow prop. Or, you could add another 4S pack to make a 12S. You'd be over current on the ground, but you'd have lots of speed in the air.
That's a 40 amp motor, so the only way to get more power without cooking it is to up the volts. With the Kv of 300 it's "geared" for a 13 or 14 inch prop. I use a 250 Kv motor for 16 inch, on my biggest planes.
Are you in need of more thrust or more speed? If both, you'll need a bigger motor.