Birm filters are typically sized for flow more so than volume. "Volume" is adjusted by the backwash frequency. Since no chemicals, salts, etc, only water is used, the regeneration frequency is not environmentaly as high of a concern as softeners are as the "waste" is only water with precipitated iron.
As to the comments that I have not said anything about changes to the 5600, and 2510, why? Is it really necessary to continue this? How many times can I say the 5600, 2510, and 7000 are all exceptional valves. The 7000 being the highest flowing, highest backwashing, and it has some other advantages that people who are not OEM's or direct distributors would not understand. The 5600 has been avolving for over 30 years, it has had many changes, all for the good. Little problems that arise, Fleck engineers look at it, and make an improvement to lessen the possibility of it happening in the future. The 2510 has never been changed? Really? I have already posted bulletins regarding the changes. Does it matter? Every Fleck valve is continually being changed, that is why the valves are one of the best in the world. Even the smallest problem (breaking collars 2510, piston seal and spacer tolerance issues, 2510, piston drive motor change from ac to dc drive, 2510, timer drive motor washer change, 2510, slip ring, 2510, etc...). How is changing a valve over the course of a decade, or three indicaitave of a product being bad. I think Ford, Toyota, Chevy, do the same thing with their products. In order to remain the best, continual imporvements are necessary.
1 more time, the 7000SXT is Flecks premiere, high flow, highly programmable, control valve that has some unique advantages to the other valves. The 2510 was my favorite valve prior to the 7000 and still remains my #2 valve, until I get a year with the 5800 to see how it is going to work out. The 5600 is the old go to valve from Fleck, the original residential plastic valve that all other valves manufacturers are compared too, and the best selling valve ever.
By using a 7000 valve, you will rarely need to worry about the possibility of having a flow limiting issue caused by the control valve should a large house use every faucet, toilet, shower etc, once a year at Christmas time when the house has 10 guests in it. It is also priced comparably to the other valves. Its only real disadvantage is that it is larger. The bypass is a full port 1-1/4", so the appearance is huge, but the odd claims of it being a foot or more longer off the back are based in fantasy land. Please see the picture below, it is a simple comparison of a 5600 and a 7000 with meters, and bypass, and plumbing connectors attached. The actual depth off the back is within an inch, the 7000 does protrude off the front more, but so what, that does not affect how close it can be installed to a wall. You can remove a few inches off of the 5600 and the 2510 by going to the electronic turbine meter, and approximately 1 more inch by using the S.S. meter. I am still trying to figure out the 12-14 inches.
Hope this information is helpful, even though it has nothing to do with the original post.