Probably this falls into topic of risk measures as mentioned by Glen. Expected Shortfall could be used. But it isn't a coherent risk measure. Entropic value at risk (EVaR) would be an option for coherent measure, if coherency axiom's are valid/important for latency measurement.

Probably this falls into topic of risk measures as mentioned by Glen_b. Expected Shortfall could be used. But it isn't a coherent risk measure. Entropic value at risk (EVaR) would be an option for coherent measure, if coherency axiom's are valid/important for latency measurement.