Well, the localy managed tablespaces are totaly different beast. The number of extents per segment is almost of no importance here, as long as the size of extents conforms with the DB_BLOCK_SIZE and DB_FILE_MULTIBLOCK_READ_COUNT. If your extent size conforms with "SAFE" algorithm you'll be just fine (SAFE method has been mentioned quite frequently in this forum, so if you need more detail you should be able to find a URL for that paper right here in this forum).