Back in the day I always used 6x3' or even 6x2's.
But I also never used high nitro fuels.

APC makes three props that seem to be good for the 049 -- there's a 5.5 x 2.5, a 6 x 2, and a 5.7 x 2.something with really skinny blades.  I have a similar engine to yours, and they all let the engine turn up significantly higher than with a 6 x 3.

The two 5.something props are good for making the plane go fast.  The 6 x 2 prop is much nicer for a "stunt style" flight -- it has lots of acceleration from launch and from hard maneuvers, but the top speed is lower.

Just get all three, and experiment.

You'll find that the prop hole is the wrong size, and that no one knows what adapter to use.  I made little aluminum bushings to go on mine.  Other people here have reported using fuel tubing.  One guy gave me an APC part number that is supposed to be good but which isn't on the APC web site -- a call to APC might be a good idea, there.

I have yet to break one in a normal power-off, no-landing gear landing, but they'll break long before the rest of the airframe will if the earth unexpectedly jumps up a few feet during an otherwise normal flight.

      Nathan , I use a APC 5x3 pretty much for most of my COx engines. I let them wind up using Sig 25%-35% nitro. Indeed the prop hole is a problem but I do use the smaller fuel tubing. I've found a piece just cut slightly smaller than the hub width works well. I put the screw through the hole and then thread the tubing up the screw slightly. I then pull the screw back with the tubing so it nestles up inside the hub then I screw it onto the engine. It works and its simple and available. I believe the Cox gray 5x3's are being made available once again. Just keep in mind the Cox gray and the APC props do and will break very easy. The 5x3 APC props are almost $4.00 a piece. I strongly suggest sanding all edges of these props as they can leave a nasty bite. Ken

Do sand the TE of the blades if you're hand starting, they're sharp as a knife blade.

I just wear my good ol' starting glove -- I've got enough funny scars on the backs of my right-hand fingers, thank you very much.