This paper extends existing analyses of the performance of heuristic search in several directions. First we show experimentally that, with minor modifications, an existing analysis of IDA* also applies to A*. Furthermore, we apply a related model to predict the performance of IDA*, using only the branching factor of the problem, the search depth, and the size of a pattern database, to the 15 puzzle. Finally, we extend this existing model to additive disjoint pattern databases. The reduction in the number of nodes expanded for IDA* using multiple additive pattern databases is the product of the reductions achieved by the individual databases. We experimentally verify this result using the 4-peg Towers of Hanoi problem. This is the first analysis of the performance of disjoint additive pattern databases.