I found the PC-to-XeniumOS FTP transfer rate a little slow compared to PC-PC (or PC-Mac) FTP across my home network after my first install. I never resolved the issue as I only used the Xenium FTP backup and then restore the C drive (and a fairly bare E drive) after upgrading the hard disk, and sending EvoX or XBMC dashboards to the Xbox HDD. Once those dashboards were configured I've used them for FTP ever since, or XBMC's file browser and a Windows share.
Wasn't particularly bothered by it, as I figured I would only use it for those minimal re-install purposes. Simply having any FTP access available at the XeniumOS level in case of catastrophic hard disk problems is enough for me. I wouldn't worry about it.
Using XeniumOS 2.3.0 on a 1.3 Xbox for the record.
Cheers