Are you using disk or tape? Looks like you may be using disk. Compression will increase your backup time. I have seen it be significant on disk backups. If you have the disk space do an uncompressed backup. If you have money buy a piece of hardware to do the compression in line. There are several of them out there. If interested I can dig up links. They are pricey though. Most can do encryption also which is a nice feature.
