WildBill said it right. SerialSARA is just a MODEM instance, you can find it in modem.cpp, 392:
ModemClass MODEM(SerialSARA, 115200, SARA_RESETN, SARA_PWR_ON, SARA_VINT);
So, you see 115200 should be ok.
I use MODEM directly to "talk" to the AT console, example:
MODEM.send("AT+UMQTTER");
if (MODEM.waitForResponse(1000, &response) == 1)
{do something}
My experience is you can NOT trust the output data from the AT console. Sometimes (as WildBill) mentioned the data get lost, sometimes its a timing problem (the sketch AND the AT console are writing at the same time, etc). I see no suitable way to solve this, the MODEM code must be faster?
Anyway, why do you want to achieve this?
PS: I still looking for contributors for the lib that belongs to this post...