The Lone Star is basically a 40X action, which is to say it is a good action. The 2500X is a new action with rear lock-up like the Win 52 and Turbo/clones. It uses an improved 40X type ignition system.
As I see it, there are two major aspects of a great rimfire benchrest action. One is great accuracy-inducing features and the other is convenience/shootability.
Accuracy-inducing functions/features such as strong and consistent ignition, full lug contact, sufficient stiffness, and good closing cam all benefit accuracy. Quality control is of utmost importance.
Shooter convenience/shootability is not often discussed/considered when discussing actions but IMO is very important for consistent BR success. The easier an action is to load/operate the faster it can be shot, which is important when one is running a favorable condition trying to get off as many shots in that condition as possible. The smoothness of the action and the amount of effort needed to close the action is important. An action that is too hard to operate or close the bolt will upset the rifle in the bags and will take extra time to operate. Excellent extraction/ejection is also important. Who enjoys digging a partially extracted spent case out of the chamber or flicking an un-ejected case out of the action port.
There is more to these "gates" then just needing to close. Otherwise we would all be using $70 Marlin actions.
In my experience-based opinion, the Stiller 2500X is the best action I have used that excels both in it's accuracy inducing features and in its shootability. IMO it is the best rimfire action that Stiller has produced. My 2500X rifle has become my primary heavy rifle and it has been a pleasure to shoot. The Lone Star will be a good platform to base a quality BR rifle around, the 2500X is better.