I had the same problem with mine. I even went the solder tube route with no real change in the mid range - idle and full run just fine, transition is perfect, but the mid was all over the place. After about 2.5-3 gallons of fuel it started running better, but still rough in the mid. Changed from Stihl oil, to the Lawnboy that is recomended, things improved a little. The single biggest thing that fixed it was putting air baffles in the cowl to direct the inflow of air over the tops of the cylinders - there are some great examples of how on the BME website. The engine runs so cool now I can touch it immediately after a flight! Sorry I dont know what the normal temperature is. The NX prop getting 6050 is about right (assuming you are still on break in, after about 3-5 gallons it will turn that prop at 6300-6400), you'll be close to 6800 with a Mejzlik 26x10, I recommend switching to it, the engine likes running in the upper 6's better, although I did like the spool up and downline breaking better on the NX, it just didnt give the vertical performance that the higher reving Mejzlik did. Kris will tell you he's turning a 28x10 at 6500, but he's on cans or drugs (suspect the latter), I've never seen one go that high - I keep inviting him down here to Texas to show me how, but no luck so far..