Without wanting to get into an “Us and Them” discussion, there are many reasons why CPU numbers may rise, no matter which program is running. These include the actual PC configuration (processor, RAM etc), running background processes, input and output buffers, number of threads invoked by the options selected.
Having said that, I’ve seen numerous streams running out of the one PC running Breakaway, with CPU utilisation no higher than 20% peak. I don’t have a comparison figure for Stereo Tool.