Dave, I will start with not all Norvel engines are the same. Knowing what version you have isn't a necessity but it could help. Not all Norvel engines require high nitro fuel. They can do exceptionally well on just 10%. However, when you run bladder, it's nice to offer slightly higher nitro as it assists in needling. I use the Cox 5x3 for a .061 Norvel on bladder. Many times, I even have it cut down to as much as 3 7/8" but for the most part, I use 4 1/4- 4 1/2". The .049 being smaller and while the 5x3 isn't a bad choice when running suction, running bladder doesn't generally like a load. You might want to try the APC 4.6x3, it's size and narrow blades might just work well as I use this combo on some of mine.
I see your aware of the Revlite version due to owning one. The reason I asked about what Norvel, some are Revlite and some are ABN which I've found that some swing the full prop while others like it clipped. The AME version vs the Big Mig also changes the equation. Big Mig versions can run less nitro and offer substantial power but the AME the higher performance version I've found requires higher nitro . When I use lesser nitro on the AME, the plug likes to cool off and I get anything from shut offs to sporadic running. I've also noted that the AME doesn't like the full size props compared to the Big Mig.
I would certainly offer less nitro on the Streak to try it and if you find is satisfactorily running, I would add another head gasket and try your higher nitro fuel once again. In general, I've always found 2 Cox head gaskets to work under my Nelson heads using 10% nitro once the engine was broken in.
The crankshaft rides in the aluminum case. The front portion of these shafts always tend to pick up aluminum and gall the case. The fragments of aluminum embed themselves on the shaft. I like to remove the shaft and polish them up using fine paper 400 -1500 grit. This tends to eliminate any drag and overheating issues that sometimes occur.
The other thing I have to inquire about is that are you using the venturi assembly with the KK spraybar? I lose the venturi and press the spraybar directly into the case leaving the gaping bathtub shaped opening. Point the hole in the spraybar directly down into the crank window and this offers some more power.