I run a 10X5 on mine, but I'm running a 240 watt headsuprc power up 450 sport motor. Its fairly comparable to the eflight motor for less then 1/2 the cost. It is a 1100kv motor though. While I was playing around with props and the watt meter, I could tell very little differance in top speed going to higher pitch props. I think the airframe isn't capabile of much over 50 mph. I'd guess I'm 45 mph top level speed.
The plane is really a floater, and even a small gust of wind can make it hard to handle if your not expecting it. I'd run whatever you feel comfortable normally and go from there. You don't want the plane to fly dfferent or change props because of wind.
I generally fly at 5-15mph winds lately. 10-15mph its not much fun. 45 seconds up wind, then 10 seconds down wind if you want to keep it semi close in a full circle.
How do you have your rates and expo setup? I just guessed on mine, and added a bit of extra rudder till I got what I thought looked right. I don't use any computer radio fancy stuff, except I did mix in the other aleroin with an extra channel. You can try adding flapperoins, but I didn't care for them much. The flapperoins just slow the plane down and require more throttle to keep moving forwards.
Here's a couple of video's to show you how well the plane can fly slow and easy once you get used to it.