V4 is EJ20K and V5 is EJ207 so they are quite different engines internally. The V5 is a big improvement in cylinder head and bottom end rigidity. We do have lots of problems with bottom end failure in JDM Sti half cuts. This is due mainly to existing damage from hard work and bad service history and secondly due to them being worked even harder once they are fitted to cars over here.
Split the bottom end and replace the bearings and you should have no problems if you run the engine on a good octane fuel.