Michael, we had a Tunze 6060 in our 90, and it worked great.
I had a Tunze 6000 in my 102g, and I found I needed more flow...but that tank was wider then the 90. I added a Seio 1500 to that tank.
Since I sold my tank, we swapped Tunzes since the 6000 was programmable, and I would loose more money selling that one. Bob now has the 6000 and it works, but I do see it could use a little more flow directly beneath the 6000. I'm not sure, but I may have even seen a little cyano starting to grow in a couple of spots yesterday afternoon.
I looked this morning, and it's gone.....so I'm not sure what it was I saw. We could also try turning the flow up a little more and see if that makes any difference.
I would say if you don't have a lot of $$ and/or don't want to add a lot to your GC...then I'm almost positive you'd be really happy with the 6060. I know Danielle has the 6060 in her 72 bow, and she's very happy with it.
Also, being you already have numerous ph's in the tank, keep one on the side.....and after you have the Tunze set up for a while, if you feel you need a little additional flow, you can always add one that you had.