File sync 2 pi's, pc's and as file server

[raspberryPI911]

I own two Raspberry pi's type B (512 MB RAM),

The situation:
2 houses with one Pi each, So SECURE communication over the web;
pc's (windows and linux) in every house;

Main Goal:
use the Pi's as Backup/sync/file server

3 goals:
-> The Pi's have to backup selected folders from different pc's (pictures from pc1, music from pc2 etc)
-> The Pi's have to sync selected folders between different pc's
-> One of the pi's has to store data (movies) which can be played by xbmc (in both houses)

Requirements
- secure file transfer and storage (except for HD streaming)
- quick enough to watch full HD movies over the internet (internet connections are fast enough)
- stable solution
- All the files that have to be backuped should be stored on a location in both houses (for example on both raspberry PI's

Solutions?
- rsync over ssh
- sftp with a (update) script on all the pc's
- barracudaDrive (not open source)
- owncloud (slow)

Thanks in advance!

[ghans]

"Secure" means encryption , and that's generally not fast on
a Pi at all. Perhaps both your routers support an old type of
VPN , but else secure HD streaming might be simply out of reach.

ghans

[raspberryPI911]

That's a good point, changed the opening post

[BobSwi]

How about AjaXplorer? http://ajaxplorer.info/nginx/