What difference is there to be seen? If your tank's ammonia and nitrite readings are zero, that's pretty much that.
This beneficial bacteria thing has gotten out of hand. There is only as much or as little beneficial bacteria in a system as there is food for it to consume, neither more nor less. And as long as there is surface area - somewhere, anywhere, the stuff will grow. I have had betta bowls with no filtration at all become "cycled." Simply put, enough bacteria was living on the glass that it consumed the ammonia and nitrite.
So really - all of this talk about mega wet/dry and mega bioball insanity is just insanity. Bacteria will live anywhere it needs to live - and while biowheels and what not will provide a very nice place for it, why go through the hassle, noise, and evaporation issues that come along with them when they aren't necessary? The beneficial bacteria will live anywhere and everywhere available to them. And if there is only so much for them to consume, they won't need any additional area to colonize because they're simply not alive to colonize it. Add more ammonia, get more bacteria. So perhaps in a really heavy stocking scenario a biowheel may be providing some additional space, but even then the bacteria has plenty of surface area such as glass, rocks, wood, plants, etc to hang out on.
The only way to hit your system's "nitrification potential" is to see how much you can overload it until it breaks. Why would you do that anyway? I mean, if the aim is to be able to theoretically overstock the tank, you're not doing yourself any favors to do so. So sure, a biowheel will give you that additional surface area for nitrification, but if your system can't handle its bioload just on its internal surface area, you're overstocked anyway. In other words, if you've made your system so that removing the biowheel will make it crash to the ground, you've made a mistake in stocking!
This is coming from someone who used to love biowheel filters - I've owned a 125, a 150, and a 400. They gave me a certain peace of mind for a long time, but that was before I learned that they're entirely unnecessary. Just a noisy evaporator. Now that I'm on all canisters with a few ACs and Whispers on smaller tanks, I see no change in anything except I don't have as much evaporation and my plants are doing better. Not that I would never encourage someone to get a Penguin or Emp filter as they're great units, but worrying about biowheels is not a headache you need to have.