Do we can use OSPF with x25 links ?
-A hierarchical topology is used
-Summarization is applied
-Zones are created
using stub areas where possible help to minimize the OSPF link state database size.
With totally stub area only an O IA 0.0.0.0/0 is sent representing all destinations outside the area.
If you need to inject routes in the remote routers you can consider to use not so stubby areas (NSSA).
Each LSA is refreshed every 30 minutes.
For this reason bandwidth comsumption is low.
There is RFC1245 that deals with relationships between number of routes and link usage
Using the right tools you can have a dynamic routing protocol running over low speed links with no issues.
Hope to help