Perform better than what? at what? The answer to your question depends on what type of shooting you're talking about, and whether or not you're talking about speed or smoothness of AF lock.
STM improves AF performance smoothness, reduces hunting, and is silent for video and liveview shooting with contrast detection--for a body that performs contrast-detection AF with the main sensor. AF performance is enhanced with STM when the main image sensor performs "Hybrid AF"; that is contrast and phase detection AF sensing with the main image sensor. So, IMO, the best body Canon currently has to take advantage of STM is probably the 70D. The 7D does not have a hybrid sensor in it and its main image sensor can only do contrast detection. It is, after all, a 2009 model, and the Hybrid AF only came in with the 650D in 2012.
However. STM is still slower than USM and phase detection autofocus (which uses a separate sensor array; not the image sensor) for stills photography. So, if "better" in your book is faster autofocus lock for, say, fast-action shooting of sports stills, then no, STM is not "better" on any camera body. I shoot an EF 40/2.8 STM on a 5DMkII and 50D. It's slower than my USM lenses to lock focus for stills shooting.