OK since we all must stay absolutely on topic here.
You have asked at least four questions (I think).
Based purely on many hundreds (thousands) of hours "loading", making, modifying, installing mapsets and data with many Garmin GPS units, but not your particular model.
No scientific measurement involved.
What does "load" mean?
Some files don't "load" at all until required. They are probably checked at "load" time.
Hence the warnings in my last post. Sorry OT again.
If by "loading'" you mean actual transferring/installing the files into flash memory.
You will probably not notice much difference if using a class 4+ card.
Using an external card reader/writer would probably be the fastest method of them all.
If by "loading" you mean the time taken from switch on until the GPS is 100% ready, navigating and awaiting your input.
Presuming we are talking time-wise here. It will take longer from an external SD card.
How much longer? Impossible to say. There are far too many variables.
Processor, software, memory speed, algorithms, data already stored, file sizes, types etc. All play a part in the end result.
If by "loading" you mean using and caching any mapset once everything is operating as expected and in actual use (navigation).
I doubt that you will perceive any difference.
Perhaps you could try your mapsets and data on both with a stopwatch and report back.
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