Just something Yvonne helped me with that I wanted to share.

When creating virtual tables that use one of the newer versions of SQL Server, be sure to use the latest available ODBC drivers.

create virtualtable vt_mytable connstr 'driver={={ODBC Driver 13 for SQL Server};server=.;uid=xxxx;pwd=xxxx' keyfield 'PK1' properties 'keepalive=1;dbtype=mssql' as select * from mytable.
The performance improvement is very noticeable.

Thanks Yvonne!!