Hi I have a clarke 135te and want to upgrade to big gas bottles. There's a shop local that deals in hobby weld but in unsure whether to get the 5%co2 or the 15% co2. 15 is a closer match to small bottles but they saying in shop everyone buys the 5 and 15 needs ordering in? It's only a day wait for 15 so that's no prob but what would be best for a beginner please? Thanks