I've flown stock K&B 4011s with a venturi and Super Tigre needle valve on several control line precision aerobatic airplanes. 10% nitro, 20% oil, 11 x 5 APC released at 9,700. I was very pleased with them.
They are the engine of choice for control line Texas Quicke Rat race. Here is link.
http://www.mecoa.com/cust/hull/index.htm