Go mullet, young man, go mullet!
I spoke to someone at the trail yesterday and he said 27.5 is better at climbing... but he has a 29er.
Maybe he meant that for any given gear ratio the smaller 27.5 was easier to turn. There was no way I could pull the steep pitches around these parts with the 32 x 42 my bike came with. Because I like high volume tyres I ended up with a 26 x 50. Put me on a 29'r I'd need a Sram 52 cog. At least.