Wow, that was an epic game! Yay for flinch hax :p. Were you expecting Thunder Wave from Thundurus? (Any non-status attack you would have obviously outsped without QA, and I don't see Taunt being too useful in that scenario.) BTW, was 4 HP / 244 Atk / 4 Def / 4 SpD / 252 Spe the "weird" spread that you said you used on your Scarf Terrakion? It's what's listed in the
analysis as the ideal spread because it guarantees survival against Flying Gem-boosted Acrobatics from Tornadus. There are a few more differences between the set you suggested and the Scarf set that Darkmalice posted in the analysis, so I'm not really sure if it would be the best EV spread for me (seems like it might not be worth reducing my damage output, albeit slightly, against everything in exchange for turning a 93.75% chance of survival against one specific threat into 100% chance of survival).