No, don't load V6.20 'coz that is US/EU firmware. For SG/MY device HWID 1193 the latest is V2.80 which you have. Info:
Code:
Please Login or Register to see the links
However, I'm now a little curious because when i was checking the Garmin SG website for the latest fw version, i see on the specs tab it's features include:

Speaks street names (e.g. "Turn right ON ELM STREET in 500 m."): yes

Lane info (guides you to the proper lane for navigation): yes (with junction view)

Speed limit indicator (displays speed limit for most major roads in the U.S. and Europe): yes

Code:
Please Login or Register to see the links
Your SG/MY 1250 seems to already have JCV, LA, TTS & SLI as standard features. What were you hoping to enable, or did you want to convert your unit to US/EU? If so, this should be possible as the PCB PNs in your SG/MY fw matches the US/EU ones, 105-01432, 105-01554 & 105-01617.

You unit will handle a microSD card up to 32 Gib without problem. Just don't exceed a 4 GiB image size.