If your game, let's try a CSV12560-3. That valve can be 60' or more from the pressure tank/pressure switch. It will only have maybe 5 PSI loss at 25 GPM, and should maintain 60 PSI from 3 GPM to 25 GPM. But that also depends on the actual pumping level in the well. It is an inexpensive thing to try, and will make a ton of difference from the CSV2W.
One option is to spilt the zones up into smaller zones and run the pump longer to get across. This is a good option unless you are already running 24/7? The same goes for people who have low producing wells. I have a 3 GPM well that I irrigate with quite a bit. I just have to run 24/7 switching from one zone to the next.
If there is a need to have more water, a larger pump is your only option. Teeing off the irrigation before the CSV will decrease the loss from the CSV2W by 17 PSI. But adding in the back flow preventer will put that friction loss right back. Using the large size zones through the CSV2W WITH a back flow preventer will require a larger pump.
I think you will be surprised how much better the pressure will be through the CSV12560-3. With this valve 60 PSI is the limit and it is not adjustable, but it will stay 60 PSI through a wide range of flow. Call Corye at the office and tell her I said to send you a CSV12560-3. If you are willing to install it, I am willing to supply it, and we can give it a try before going to a more expensive alternative.
I love how you have documented everything, which will be a great way for people to see the difference in performance of the CSV2W and the CSV125. Many people think the heavy brass CSV2W valve is better than the plastic CSV125 valve. For longevity and handling debris it is, but for performance it is not. I use the CSV125 myself, because it has the better flow characteristics than any valve I have, including the CSV3A2T.