Lets face it, most of us know by now that bikes like the Specialized Enduro 29er (S-works) and Santa Cruz tallboy LT (Carbon, high spec) crush all the competition when it comes to all mountain bike reviews. They are amazing bikes jam packed with the latest technology and they can do it all, climb and descend really well and they aren't too heavy to spend all day on and don't hold you back on long distance trail rides. The point being that bigger is usually better BUT only if you can afford a high spec bike. 29er wheels are HUGE and the problem with less expensive wheelsets on 29ers is that they are heavier and not as stiff. Both of these factors are critical on a bike. Imagine the exact same bike with the exact same components and then evaluate them with budget, mid-range and high end wheelsets. As the wheelsets get cheaper you will notice the issues with a 29er, flex -> tracking, acceleration etc. So, my decision to buy a 27.5 ultimately came down to this. I found that riding a 29er (that I could reasonably afford) I could really feel these issues when I pushed the bike. I'm sure if I had the money to buy something fancy I wouldn't have found it a problem and would have loved it. So when I test rode a mid-range 650b bike I found it handled great, accelerated well and I didn't notice flex in the wheelset, fork, frame etc that I would on an equivalent spec 29er. So, if you have a load of money, (like 5-10k) buy a 29er. Maybe a Specialized Enduro 29er S-Works etc or something else equally pricey with a great stiff light carbon wheelset and top end fork. But if you are just spending 3-4 grand, go the 650b and I think you will be happy. IMO they really offer the best of both worlds for people who don't have all the money in the world.