Runtime quality of software, such as availability and throughput, depends on architectural factors and execution environment characteristics (e.g. CPU speed, network latency). Although the specific properties of the underlying execution environment are unknown at design time, the software architecture can be used to assess the inherent impact of the adopted design decisions on runtime quality. However, the design decisions that arise in complex software architectures exhibit non trivial interdependences. This work introduces an approach that discovers the most influential factors, by exploiting the correlation structure of the analyzed metrics via factor analysis of simulation data. A synthetic performance metric is constructed for each group of correlated metrics. The variability of these metrics summarizes the combined factor effects hence it is easier to assess the impact of the analyzed architecture decisions on the runtime quality. The approach is applied on experimental results obtained with the ACID Sim Tools framework for simulating transaction processing architectures.