With the slightly longer rear end a-la B17 then 27.5 goes in no problem with a conti 2.4 tyre. Couldn't say about the standard swingarm for sure.
The 29 WTB tyres are 2.1 and that works fine. I tried a Spesh Butcher 2.4s and the rear fouled on the seat tube before the shock reached the end of its stroke. A Conti 2.2 seems OK but clearance isn't huge.
It rides well considering, still tuning the air pressures. It feels tall, if that makes sense. I have yet to try it properly, only been out with the kids recently but next trip out I'm taking this with the 29 inchers to see how it goes. I'll update when I have an update.