1. A method comprising: determining a network transmission time of data transfers between an end user and each of a plurality of tiers of a multi-tier system; calculating a first response time of a first tier of the multi-tier system using a first model; selecting a second model that is different than the first model, wherein the second model is selected from a set of models that includes a load balancing simulation model and a regression analysis model; calculating a second response time of a second tier of the multi-tier system using the second model, the second tier including at least two partitions; determining an aggregate response time based on at least the network transmission time, the first response time, and the second response time; and reducing the aggregate response time based on a probability factor indicating a probability that at least one of one or more front end (FE) servers of the first tier or a back end (BE) server of the second tier fulfills a request using previously cached data.