I've never used it but what about sys(3050)?

MSDN Library says -

SYS(3050) allows you to optimize Visual FoxPro performance by adjusting the amount of memory Visual FoxPro allocates for the foreground and background buffers. The foreground memory buffer is the memory available to Visual FoxPro when it is operating in the foreground as the currently active application. The background memory buffer is the memory available to Visual FoxPro when it is operating in the background when another application is the foreground application.