350mA is a specified testing parameter from which a spec is determined, 2000mA is the manufacturers max recommended current to run the LED at.
But, this is BLF where people push the limits. Welcome 
Here is a test by a member proficient in testing LEDs, have a look to see how far he pushes an XP-G3:
https://budgetlightforum.com/t/-/39933
LEDs come in different variants though, different bins, different colour temps and with tolerances etc so the test won’t exactly represent any XP-G3 you buy but it will give you a very good idea of what to expect.
Also, you can talk to us so we can help you figure out what a ‘bloody bright flash light’ actually is, show you some options of what’s available and advisable, point you towards reviews and the beamshots that say more than a thousand words, and even advise where you can buy from.
For example, i would recommend a different LED for a bright single AA light than for a bright 21700 direct drive Li-ion light because they have very different power requirements.
For a reference point, what torches do you have experience with?