Lower baud rate to 115200

While things appear to work OK at 230400 I do run into the odd issue from time to time that leads me to believe it's something with the serial connection.

According to this https://copperhilltech.com/blog/rs232-to-usb-converter-with-arduino-due-or-mega-2560/ the maximum baud rate for the Mega2560 board is 115200.

Interestingly this post https://arduino.stackexchange.com/a/6865 provides the following:

Baud Rate   UBRR(dec)   UBRR(hex)   % of error
300 3332    0x0D04  0.0
600 1666    0x0682  0.0
1200    832 0x0340  0.0
2400    416 0x01A0  0.0
4800    207 0x00CF  0.2
9600    103 0x0067  0.2
14400   68  0x0044  0.6
19200   51  0x0033  0.2
28800   34  0x0022  0.8
38400   25  0x0019  0.2
57600   16  0x0010  2.1 - Barely OK
76800   12  0x000C  0.2 - GOOD
115200  8   0x0008  3.7 - BAD
230400  3   0x0003  7.8 - BAD
250000  3   0x0003  0.0

According to their calculations the fastest the Mega256 can go with a sub 1% error rate is 76800.

I think I'll have to do more digging.