The default size of the 7000SXT is a 32MM manifold assy. The 1.05" which is the same size as 3/4" PVC is the standard for most other controllers. The 7000 can be ordered with the smaller 1.05" adapter installed, but this adds a non servicable o-ring on the adapter pt#61419, not a great idea, but we have never had a problem with this o-ring yet. Once this adapter is installed, it is not removable ( at least not unless you can use a small hacksaw blade and about 15-20 minutes of time) There is absolutely no disadvantage to the larger valve, manifold and screen assembly. Future valves from Fleck will likely start moving toward the 1" PVC pipe spec instead of the 3/4" pipe spec. I would not be surprised if the 7000 moves away from the 32MM spec and goes to the 1" PVD pipe spec, (a bummer since we own the tooling to 32MM pipe for the West Coast)
The 2510SXT is more expensive than the 7000SXT. Even the electromechanical 2510 is more expensive than the 7000SXT. The meter on the 2510 is also not as strong or durable as the 7000's. The meter replacement cost is far less expensive as well. The meter on the 2510 is an external sandwich style meter used on the 5600, 6700, Pro-Flo etc., the 7000 uses the same meter as the larger commercial valves like the 9500 and 2850s.
The 7000SXT has eliminated the need for several valves of the Fleck line, especially since it has higher flow specification, higher backwash rate capability, optical positioning (eliminates the need for micro-switches), NEMA 4 outdoor rating, and a lower price. I am a huge fan of the 2510, but our sales have dropped to almost nothing except for the AIO version of this valve. The 7000 is a better valve, lower cost, newer design.
Again, either valve will provide you with 10-20 years of trouble free life, you will be happy with either system. I just dont see a need for the 2510 anymore except for spec'd units in qualified applications where the requalification process can cost 10's of thousands of dollars. That is why we still use the 2750 in so many applications, it was qualified into the specifications for USP 27 , Dialysys, WFI, or other applications and the requalification process is too expensive and time consuming.
The 7000 also has a better collection of plumbing connectors available. 3/4" - 1-1/2" MNPT fittings, 3/4" - 1-1/2" sweat are all available. The 2510 is limited to 3/4" - 1" MNPT, and 3/4"-1-1/4" sweat, but the 1-1/4" sweat connector looks like a pair of binoculars.