You could very well be going too wide. My sit bones measure 134 and looking at the Specialized chart my perfect saddle for road riding is supposedly 155 for everything apart from an extreme time trial position. I tried a 155 Ruby and had the same problem you had.
However, I'm now starting to question the sit bones plus 20mm rule as I'm presently riding a saddle that's only 135mm wide and my pelvic bones are directly on it.
Look at the Steve Hogg site where he discusses SMP saddles. Even if you never plan to try that particular saddle, there are two very good photos of a plastic pelvis sitting on a saddle that explains why sit bones don't actually contact a saddle unless you are bolt upright on a recumbent or pedal-forward style bike.
http://www.stevehoggbikefitting.com/...ll-about-smps/