Re Handoff in Yosemite... there are hacked kexts that make it work just fine in older (non BT LE/4) Macs (with regular BT) making it fairly clear that an artificial limitation was introduced.
That's not quite the whole truth. There are two Mac models where you can simply enable it: the mid-2011 Mac mini, and the mid-2011 MBA. Every other model it could potentially work on, you literally need to upgrade the wireless card.
Given that, it makes me wonder how the unmodified Mac mini and MBA perform.
Given that, it makes me wonder how the unmodified Mac mini and MBA perform.