We examine the superfluid phase of a hard-core boson model with nearest-neighbor exchange and four-particle ring-exchange at half filling on the square lattice. At zero temperature we find that the uniform superfluid in the pure- model is quickly destroyed by the inclusion of negative- ring-exchange interactions, favoring a state with a ordering wave vector. Minimization of the mean-field energy suggests that another type of superfluid state, characterized by nonzero bond chirality, is formed. We also study the behavior of the finite- Kosterlitz-Thouless phase transition in the uniform superfluid phase, by forcing the Nelson-Kosterlitz universal jump condition on the finite- spin-wave superfluid density. Away from the pure point, decreases rapidly for negative , while for positive , reaches a maximum at some in agreement with recent quantum Monte Carlo simulations.