For whatever its worth, I think that the "fun factor" and the "learning factor" are key for deciding when to raise the white flag. If the game is early on, and, even though my armor is toast and my arty spotter was wiped out, well, I might just keep going because a) I might pick up some experience/knowledge by playing the underdog and b)It might still be entertaining for me to play out the string, and certainly more so for the opponent.
On the other hand, in your situation when things are hopeless and the other guy probably considers it to be unchallenging mopping up, then I'm all for cutting your losses and getting on to another game in the search for redemption...