Overlay networks have been shown useful for improving the delivery of network and processing resources to applications, in part due to their ability to use alternate or parallel network paths and computational resources. This paper presents IQ-Paths, a set of techniques and their middleware realization that implement self-regulating data streams for data-intensive distributed applications. Self-regulation is based on (1) the dynamic and continuous assessment of the quality of each overlay path, (2) the use of online network monitoring and statistical analyses that provide probabilistic guarantees about available path bandwidth, loss rate, and RTT, and (3) a packet routing and scheduling algorithm that dynamically schedules data packets to different overlay paths in accordance with their available bandwidths. Additional aspects of IQ-Paths are its predictive statistical bandwidth guarantees and the fact that packet scheduling across different overlay paths is governed by application-level specifications of stream utility. An example is to send control data across links that offer strong guarantees for future bandwidth vs. mapping other data across less guaranteed paths. Experimental results presented in this paper use IQ-Paths to better handle the different kinds of data produced by (1) distributed multimedia applications with desired QoS guarantees and (2) data-driven or interactive high performance codes with user-defined utility requirements.