The actual string sent is:
:MEAS:FREQ? 311MHz, 1Hz, (@2);
I've just read the NI white paper on the termination topic here:
http://www.ni.com/white-paper/4256/en/
It says "For VISA resource types that correspond to a complete 488.2 protocol (GPIB Instr, VXI/GPIB-VXI Instr, USB Instr, and TCPIP Instr), you generally do not need to use termination characters, because the protocol implementation also has a native mechanism to specify the end of a message. You need to tell VISA how messages are terminated only when using other VISA resource types (Serial Instr, USB Raw, and TCPIP Socket)."
So I guess I won't mess around with this, given that we're using GPIB.