access to common files at 2 sites

I'm sure this is a common requirement and question has come up before

Single company but 2 site - linked by slow internet connection

Internet speed is EFM (Copper Lease Line) 10mbps

Files are large 30mb (some 100mb+) as well as small word / excel files
plus large CAD files

both sites need access to each others files

rsyncing overnight - sort of works.
After syncing both sets are marked read-only

like I said this work ... up to a point!

Does anyone know of any BETTER solution which gives Read/Write and file locking !

looking into Filr but I don't think will cut it... I don't want thousands of files littered on users notebook / pc's
plus there could be Conflicts to deal with

anyone using SureSync or similar http://www.softwarepursuits.com/sure...FY_MtAodim8AUw ?

looks like it might do the job but would love to hear from anyone using it or similiar products.