Heroic dungeons = LFR
Challenge mode = Raiding
It should require planning, teamwork, CC and doing mechanisms correctly.
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Basically you will get your heirloom, but continue using your heroic SoO weapon this expansion.. Next expansion, maybe level 91 or 92, your heirloom weapon will be an upgrade over your SoO weapon and then you can use that heirloom all the way to 100. ( since the heirlooms scale to 100, it is a good bet the next expansion will take us to 100)