What render engine do you use ? On the supported engines (see our Rendering Best Practices guide.
), it should not be problems rendering huge objects.
RailClone has not an equivalent to Forest Pack's Limit to Visibility feature, because the position of segments in RailClone is always dependent upon their position within the array, so it is always necessary to build the entire array to calculate the position of each segment correctly.
Anyway this is not a problem, because initially the plugin doesn't calculate the entire geometry for each segment, but only its bounding box (this process is very fast). Once in render, the geometry is processed dinamically and using instances where possible.
If the problem happens only with a certain style, please send us a test scene. Possibly it can be optimized to improve the instancing efficiency. You can see the technical details in the above link.