I must say I enjoyed Mavericks more, but perhaps after another few months Apple will get the bugs sorted out of Yosemite. Speed wise I have no desire to benchmark this until it's functionality is sorted.
The reason why is because I went to the Apple Store, and used Yosemite.
I know I've hated on it in the past, but I can't lie, it was pretty nice!
I was thinking of MAYBE upgrading, but I don't want my computer to slow down.
I have a 2.6GHz processor like the current gen except mine is late 2013. So I'm guessing it should be the same experience.
I hadn't noticed any performance degradation, but then I wasn't looking for it either. I like some of the features of Yosemite like the improved search.
If there's no reason to move on to 10.10 and you're happy with Mavericks, hold off.
I have the exact same mid-2014 model in your signature and I upgraded from Mavericks to Yosemite and I can tell zero difference as far as speeds.
I did not do a before/after benchmark with any utilities or anything, but in day to day usage I don't feel any difference at all.
What exactly do you mean by "faster"? Yosemite does ship with some optimisations in its UI framework and it GPU drivers are significantly faster (as least for Nvidia and Intel hardware). No idea in regards to memory allocator, but I'd expect some optimisations here as well. But it should be clear that no OS can magically speed up your hardware, so there can be no improvements in CPU-heavy applications.
Now, if you are talking about 'faster' as in 'snappier UI on retina machines', then yes, Yosemite is a clear improvement at least on all machines that I have installed so far. However, it seems that many people are having performance issues.
I'd say: if Mavericks is working well for you and you don't need the new features of Yosemite, then do not upgrade. Software should be Mavericks-compatible for at least next year until people start actively using Yosemite+ APIs.
By faster I mean opening apps etc.