e.g. my current main system has a 990FX AM3+ motherboard with a Phenom II 1090T CPU...I haven't bothered upgrading it to an FX-8350 piledriver CPU but will probably upgrade it to a steamroller CPU next year.
I can understand why. It's rare (maybe 45 minutes in a month, always when encoding video) that I can keep all 6 cores pegged on the 1090T. If it's a Black Edition, it will happily run all 6 cores at the Turbo speed provided you upgrade the cooling (which is advisable for the sake of your ears anyhow). The real advantage over the quad-core is that you can pound on it, but it still has just enough power to respond to requests in a reasonable manner.
I don't overclock mine any more just because it's too damn loud, though I would if I did more video encoding. The extra heat from running at 3.6 instead of 3.2 makes the exhaust fan spin up, and at 4 GHz (+0.0775V) it will eventually heat to the throttling point which is obviously counterproductive. The (2 x 120 mm) CPU fans CAN'T spin up. I locked them at 100% because I can't hear them over the other fans at all, unless the case is open. Why throw less air at the CPU if it doesn't produce a tangible benefit?
I've considered getting more exotic cooling so I could choose between stock and near silent, or significantly overclocked but loud. Better still would be to put it in an adjacent room but I can't currently cut a hole in the wall to route the cables though. I did that in the last place though.