Be sure you know which controller you are getting. If its the "multicontroller" that looks like a good deal. The Stream pump by itself is US $308 (the 6100) and the multicontroller is US $202. If its just the "single controller" you are talking about $55 for it.
Now, as for your question, let me qualify this by saying I don't own one yet, but I'm setting up a 48x30x30 and I'm going to use 2 6000 pumps and a multicontroller (the 6000 has about 58% of the flow of the 6100 and I could do any kind of closed loop if I wanted to). This after much research on the reefcentral.com Tunze and other forums. Ask for Roger Vitko on that forum, he is the real deal on customer service.
Bottom line, based on my research, one 6100 stream won't be too much at all. With your return, a lot of folks would go with 2 of these on your size tank, assuming they are doing at least mostly SPS and have taken a few sandbed precautions (working up to max flow with the multicontroller, etc.) Drawback is the stream is kind of big and ugly. That's it. Positive is low power consumption, about 45W, you can move it around (especially with the new magnet), quiet, little heat, no drilling, big wide soft high volume flow, blah, blah...Oh and the output for a 6000 like I'm getting is like 2'x2'x2' so its not like a jet or anything, I can't remember the dimensions of the 6100 but according to the forums I read people put hard corals like maybe 6" in front of the stream (after acclimation). Its a very wide, high volume flow, not like a jet at all.
Good luck mate.
