[voltagex_]

Use POST. GET is not meant for that amount of data. Alternatively, GET by a shorter ID.

[lollerpops]

What do I do about the people who tell me POST is only for actions which change server state?

[voltagex_]

You write a well documented application that is useful, adheres to as much of REST as you can and leave the theories to other people.

[drivebyacct2]

Simultaneously, it seems to indeed be a convention. And why not follow it? Do you have something whose keys really require the numerousness of 8KB of characters?