At 3800 kvm, I'd suggest something in the 5X4 range if you're not going to use a gearbox. A 10X6 is something you'd run with a motor in the 1200 - 1400 kvm range. Otherwise you'll be pulling more amperage than that motor can take. Take a look at the Hacker website, for their specs, they suggest that prop if you run a 4:1 gearbox.
http://www.hackerbrushless.com/motor...plication.shtm