I have one possible explanation for such a phenomena to happen that cooling might make a 286 run faster. What may have been happening is that cooling the CPU shifted the timing of the CPU which is very plausible, this may have affected the system control circuits that terminate the cycles if something was right over the margin of timing. In some cases a slight shift in timing may advance the terminated T_COMMAND of the 286 into one CPU clock cycle earlier. That could theoretically result in a significant faster performance. Imagine one T_STATUS and for example three T_COMMAND cycles, a total of 4 CPU cycles that were executed previously, shifting into one T_COMMAND earlier, this would result in 1 T_STATUS and 2 T_COMMAND cycles, and increase the efficiency of the CPU by 25%.