The spools in a pilot-actuated solenoid valve will only need to move around 0.040 inches to shift. The design of the spool is more intricate than that of most mechanical three-way valves, since the solenoid doesn't have an o-ring that has to "cross over" an air port like the three-way valves do (most of them anyway). Instead the spool has thin o-rings which only need to be unseated to expose the air port, then another o-ring seals it off on the other side...the result is shorter travel amongst other things.
That would be the general rule for most solenoids used in paintball that employ a pilot valve (generally most Parker, Humphrey, ASCO, and SMC solenoids that we use fall into this category). The big exception in paintball is Mac valves, most of which don't use a pilot. All the aforementioned companies make solenoids in both pilot and no-pilot versions, but for the paintall application we end up using ones that have a pilot for battery reasons (also for their small size).
If you check the datasheets for the solenoids you have on-hand, oftentimes you can find a cutaway drawing that will give you an idea of how far the spool travels. Airsoldier.com hosts a lot of the datahseets you would want, or datasheets for similar valves.
^^ very similar to the Parker solenoids in terms of layout