As for fire, we have an open fire at home and I don't mind putting this test piece into it, I may be month or so until it gets cold enough in the house to light it, you may have to wait for those results, the best I can do is phone the supplier of the metal and ask what the metal spec was for our best guess at a melting point, although it will of course soften before that.
quick search says fireplaces can be 500F-1100F depending on fuel etc. house fires can be 1100F. a propane torch can hit 2000F. so if you can test it with propane torch (which are very cheap) and heat it to red hot say and have it survive that would be a good test.
I can use a propane torch and get it to 2000F but I'm not sure that's a fair test:
Using the propane torch to me seems more like a test of the metal quality/spec than proof of survivability. I could easily have spent 8x more on really high quality steel/titanium/tungsten to be certain it would survive but that takes it out of the realms of an affordable home project for most people.
I got the metal business cards from ebay, and as it's a prototype it was on the cheap. I think all steel has a melting point above what my open fire produces (and a house fire), my concern is that the card softens and distorts before that melting point, if it does I would consider it a failure.