Update: Just put 10 shots through the chrono in a more ambient temperature and saw a massive improvement. The mean Fps being 562 with a standard deviation of 4 Fps (JB really does make these rifles go up another level). That equates to a
mean of 11.24 ft/lbs with AA field 16grn.

I will rarely be shooting at -2C (temp i chrono'd at last night) but its good to know that even in the extremes I lose less than 1ft/lb of energy. Forever learning aren't we!