No, we ran an extensive benchmark against log data and found that simplejson was indeed 10x faster. Your benchmark assumes a different "shape" of json dictionary than ours, and I would recommend updating your methodology to use real data instead. I added ujson to our benchmark, and here are the results (seconds):

$ python json_bench.py history.log.1 json 106.270362854 simplejson 11.336577177 cjson 5.63336491585 ujson 3.81600308418