I'm trying to edit Rd3 files in Adobe Premiere pro cs5 I cannot afford to upgrade at this moment. What are the alternatives? Should I export from Redcine X? If so what are the settings that I should follow to edit in cs5? I would be editing at 1080.
It depends; you really need to list your hardware since CS5 speed for various formats is impacted by cpu, gpu, RAM, and drives.
If you final result will only be 1080, then you can certainly downsample up front to ease the work your PC has to do. OTOH, if you ever want to export with the full glory that Rd3 files are capable, editing the Rds files natively is probably the best workflow.
Have you tried changing the playback window resolution way down?