Usually cocktails (mixing) of any drugs will have an increased effect. I do tend to notice that taking a different kind of opiate, even though my tolerance is quite high, will have a better effect. My theory on this is that, in your case for example, you may have a tolerance but also you are used to the feeling and know what to expect. When taking another substance that you are not so familiar with, in my humble opinion, will be more noticeable and therefore increases the effect more so than if you were to, say, take more hydrocodone rather than mix the two. Also whenever safety is an issue you usually only have to be concerned about mg of acetaminophen, so be sure you are well under 4000mg/24hours and you shouldn't have any problems, I've had up to 8,000 and I can tell you that you'll feel like shit regardless of how much hydro or codo or oxy came with it.