Range using single-mode SFPs across multi-mode fiber

Thanks to all who responded to my clumsy first question (both on matters of etiquette and technology). The group I work with (we are a small project acting as a last mile provider) was in the midst of deploying this solution when I posed the question. We put the single mode Juniper SFPs (LX) on to a run of approximately 1670 meters. We successfully established a 1G ethernet connection. Testing to date has been meager, but shows that the link is viable. Under significant load there is some minor packet loss. Since the link far exceeds the amount of data it required, we have decided to continue using it. Interestingly neither interface showed any physical errors. v/r, Oliver Rothschild Network Engineer III