The Australian manufactured powders had heat stability in mind, whereas the American manufactured Hybrid H-100V from St. Mark's Powder (General Dynamics) did test this stuff for use in extremely cold conditions. The test consisted of a high altitude, cold temperature blast, where the overpressure created by an air burst of a ton of powder was measured. There might be some debate as to the correlation between such a test and the charges typically fired in small arms cartridges, but it makes for interesting reading anyway. To my way of thinking, muzzle velocity is the only measurement that matters when a powder is used in the cold, as cold dense air effectively reduces a bullet's BC. Since chronographs, at least those that are affordable to individuals, develop accuracy problems under cold conditions, and since the bulky clothing necessary in the cold, interferes with the LOP of the rifle and causes parallax issues with the scope, and as previously stated, dense air reduces BC, and since the primer used may or may not be the best suitable for the conditions, the exact cause of a steeper trajectory in the cold can be difficult to pin down.
