a) I think no, performance will not improve if you have nine SQLGateways.
SQLGateway ODBC connection is established in each process.
So each separate Caché process has each own connection to the SQLServer.
b) As to the SQLGateway performance. I think first thing you need to check is how SQLServer itself handles these nine queries being run simultaneusly. If it's fast, and slow only via SQLGateway connection, then it makes sense to look into if something can be configured on SQLGateway / Caché side.