I was hoping to get information about the stability, speed, etc

As VFP is not a DataBase server itself, all the processing of the tables will be on the SQL Server. This, included with slow speed of the ODBC (OLE DB) access to VFP tables (as Sergey Berezniker said) will make the approach with linked VFP database in SQL Server not to have many advantages compared to our approach. We query the VFP tables and make some preprocesing and after that create queries to the SQL Server databases. Or depending on the case, the sitiation may be the opposite (this is not typical for our design) - first quering the SQL Tables and after that the VFP ones.

All queries are make in ANSI SQL format, and due to some differences of SQL Server and VFP they are "converted" in proper syntax from our specific tool.

HTH