Peter,  I have an Enya 40xzs  that I can say I am very pleased with.
After several bench runs I mounted the engine on a Brodak P40 ARF.
Engine is a one flip start consistantly , very smooth and more than enough
power for this size airplane.  Nice 4-2-4 type run with my set up.
Setup :  Fuel is Excalibur 71/2 nitro, 11% casto and 11% synthetic.
            Prop is a Zinger old style 11X5 wood prop.
            Fuel tank is a GRW 4 3/4 oz uniflow, now sold by RSM Dist.
             (4oz gets me through the pattern)
             Fox spinner nut
             Stock muffler very quiet
             Fox standard long glow plug , no drop in RPM when
             battery is disconnected.
             Fuel filter is a Brodak metal screw together type.
 I have approximately three hours on this engine at this time.
             

I havent tried one of this yet, but I am getting awesome performance from my Enya engines using 3 blade low pitch props for piped engines.

The Enya SS50 is working with a 3 blade 12.5x3,75 and the 61CX with 3 blade 13x3.75. Both can be setup to run 4-2-4 or 2-2-2 and if you put in a light model I donīt see why it would not work 4-4-4.

The 3 blade 12x3.75 did not load the SS50 enough, it went like a bullet and  it needed the 12.5x3.75 one.  The Enya 61CX is the friendliest most powerful engine I have ever seen for C/L,  it works with any prop any venturi size and it will carry huge and heavy models.

The Enyas are not stunt detuned, they are similar to Magnum 36. So my guess is that you could get  killer performance out of the Enya 40XZ using a 11.5~12x3.75 3blade prop.

The Enyas come with a small venturi, to get more power I recomend using a larger venturi.  I use a 8.0mm with Enya SS50 and 8.5mm with the Enya 61CX.

I bet the 40XZ  will work mighty well  with a  7.5mm venturi

Martin