The thermal conductivity of GELID's GC-4 thermal compound is not officially published by the manufacturer. However, based on the information provided and the measurement graph, we can make an estimate.

According to the graph, GC-4 is slightly better than GC-Extreme, which has a known thermal conductivity of 8.5 W/mK. This suggests that GC-4 likely has a thermal conductivity that is higher than 8.5 W/mK but not as high as Thermal Grizzly's Kryonaut, which is rated at 12 W/mK.

Therefore, it's reasonable to estimate that the thermal conductivity of GELID's GC-4 thermal compound is somewhere between 8.5 W/mK and 12 W/mK, with a value likely closer to the 8.5 W/mK end of the range.