I recently experimented with a pair of Fat B Nimbles on my Karate Monkey, and I'm not sure its the answer. My rim is 33mm outside width, and I'm feeling a bit squirmy in the corners compared to the 2.4 Ardents they replaced. Maybe with wider rims they'd feel more stable...I progressively aired down on my local ride and when I got to the point of feeling the benefits of the almost plus size volume, they weren't confidence inspiring during hard cornering. I paid $108 shipped for the pair brand new, with one Surly 3" tube included, and I'd pass them along for $100 shipped if there's interest.
It's also common for me to hate new things for a bit, then change my mind and be totally stoked. Maybe I should give them a second ride....