My tank is about the same size as yours (90g - 36x30x20) and one gyre was enough flow, but not as random as I wanted. So I pulled the gyre and went with 2 wavemaker instead. The total flow is about the same, but it's WAY more random and always changing rates and directions. I like it much better.
This photo is from before I even added the gyre. But I have 900 gph of flow out the 4 lineloc nozzles from the return pump.