I installed Windows 10 technical preview on my late 2013 rMBP on an external USB 3 hard drive and the performance is actually smoother than Yosemite. I may have to consider installing Windows 10 on the internal hard drive when Windows 10 comes out and if 10.11 doesn't fix performance.
It's soooooooo buttery smooth.
It's soooooooo buttery smooth.