Well . . .yes and no. You are incresing the flow, but remember that when you add an airline to a pump, it drastically reduces the output of a pump. So keep that in mind. Plus, a more efficient venturi will produce more bubbles than the RIO. So while you may have less contact time, there are more bubbles. IMO, it is a worthwhile trade off. Because the bak pak isnt that tall to begin with, I dont think that increasing the flow from a rio to an mj would really make that big of a difference on contact time. Now if you were talking about one of those huge floor models that are four feet tall, that would be a different story.
HTH
Justin
P.S. let me know how it works out. I have considered changing to a MJ as well, but I like me preskimmer a lot so, it would have to be a significant improvement.