Nope. It will still drop below 60 when shit hits the fan. For example on Ultraxion 25man, or trying "more whelps" achievement at Onyxia... Or when 3 raid groups are killing Oondasta. Or when you're sitting in Orgrimmar/Stormwind 1h before raid time in a "full" realm. It's not a problem of WoW alone, but whloe MMORPG genre. MMO in it means you might run into a situation where the game client simply chokes from having too many players in the same zone.
You can achieve 50+ fps 99% of the relatively easy, but getting 60+ fps 100% of the time will not happen with any kind of system unless you're willing to drop the graphics settings.