Is the physical size of each pump different from one model to the next, or are they all the same size?

They are slightly different. You can find the dimensions on the Tunze website:
http://www.tunze.com/usa/index.html?lang=en-gb

You can kinda tell it's a German site translated into English but if you navigate around you'll eventually hit upon the Stream models and dimensions.

Interestingly you can't find any info on the soon-to-be-released products but if you surf through the MO vendors like premiumaquatics you can get a general gyst of the features.

Hi. I have the TS24 kit tunze in my 500 gallon reef, included is the multicontroller, photocell, and capability to operate more tunze stream if needed. This kit pushes around 3175 gph each stream. Recently one of the stream impeller broke and cause the alarm to go off. Too late, the damage was done already though. Fortunately I have a backup like everything else. I am very happy with the tunze TS24 except the cost. Regards Ken

Tunze
 

Got any pictures of that tank Ken? We'd all love to see it.

Hi Jaws, sorry for no pictures. My computer skill lacks in how to picture. But eventually I will get someone to do it for me. If you are ever coming up north of the island let me know, because I spend alot of time in the fish room. You are welcome to view it live, nothing fancy, just the typical reef. Oh by the way, the reason why the impeller broke, is probably due to my fault. They were never serviced since new 2 years ago. The coralline encased the entire pump. Another TS24 kit will also be added eventually when I get around to it. Regards Ken