This is straight from
WoW Insider:
Low-end epics will be replaced in most cases by level 71 or 72, but can sometimes last as far as the mid-70's. High-end quality epics will carry you quite a bit farther, to level 78ish, and in many cases, all the way to level 80.
I know that item stats haven't been finalized yet in the beta, and with a few tweaks, all of this could change. But for now, forecasting the future as best I can, this seems to be the pattern. Should you continue, in these final months of the Burning Crusade, to grind out gear upgrades for your Characters? I'd say absolutely, positively "yes."
If your Character is in a progressive raiding guild, continue the push. Sunwell gear will in most cases trump anything you find before the new end-game. Those epics your guild worked so hard to earn will help you gain the next ten levels and only be replaced as you gear up to enter the expansion's first raid.
If PvP is your thing, you won't find much worth ditching that Brutal Gladiator's set for until you get to the level 80 season 5 set. It's possible that you might encounter the odd piece that tempts you to break the set, but we won't see anything similar to what we saw at the beginning of the last expansion. You certainly won't want to drop your high-end purples for anything you'll find in the first few zones of Northrend.
So rest easy. Your epics will have value when Wrath hits. There simply isn't going to be any sort of hard gear reset this time around. Tell any guildies who might be resting on their laurels, waiting for the expansion to hit, that they need to get off their butts and keep pushing. Black Temple gear, Hyjal gear, even Zul'Aman gear, will last you substantially longer than Kara gear, so get moving. Get that raid organized or puff up that Arena rating, so when the expansion comes, you can blow through it like the glass cannons you are.
