I've been thinking about mixing these two pumps as well in a future 5 or 6 foot long tank.
My idea was to put the Gyre pumps on the rear wall, up high & Vortechs at both ends. I would be looking for the ability to get some current flowing directly at the rock face for at least a few hours a day. Based on the videos I've seen of the Gyres, I think this would work but would need to do some experimenting first I'm sure. Your idea may turn out to be the best way to go.
I think a short period of broad, relatively high current, coming straight at the rock face will be beneficial. It should dislodge detritus that can stay put with only left to right & right to left currents.
I recently did a major maintenance on my 6 year old tank. I used a power head to blow off detritus, getting it into the water column for mechanical removal. The frontal current dislodged a huge amount of junk from the rock face and behind the main structure. I was astounded at the amount of junk this stirred up, even though I regularly clean off rocks with a turkey baster & siphon it out during water changes. In my mind, this may be a precaution for avoiding "old tank syndrome" and future nutrient issues. Plus, I think mixing these two power heads would provide some really crazy random flow. The only problem might be keeping the sand bed stable.
In my current tank, I am going to occasionally mount my current MP40 on the front glass from time to time and observe the results.
