The new kernel fixes the RC5 issue, so existing fixes should be removed.
Read the RC6 "release" notes, and the announcement topic and users followup reports.
rsync by default uses ssh, which by default uses encryption, which requires a powerful CPU which the box don't have.
Everything that requires encryption or compression will be "slow": ssh, rsync, ftps, sftp...
The exact "slowness" depends on the particular box model, the 323 being the slowest with some 1.5MBps to the 327L with some 6MBps for ssh.
For your particular case, it's better to do a mount using NFS or CIFS and run rsync locally, as that will not involve encryption nor compression -- that's what the native Alt-F backup script does, use Services->System, Backup.
If internet is required, encryption should be used and a faster and less secure crypto algorithm such as arc4 could be used.