I don't know anything about the arcadia bulbs- I'd certainly trust Hoj's advice though. But if it's a choice only between the bulbs you are asking about- 5.0 will get the job done safely. Some of us (me for example) use 10.0 and I haven't seen an actual reported problem from their use, but 5.0 is enough when used properly (if you have a big cage- get some branches up near the bulb and away from it as well) and 5.0 has a great track record of success.