What
tank are you using them in? I find 1.8 ohm are good 7-11 watts and I have heard 1.5 ohms going good to 15 watts. By the way it seems, possibly 13-18 watts would be my suggestion. Start low and bump it up a little at a time. start 11 watts, few hits, then 12 watts few hits and so on. When you notice a slight burnt taste, back it down a little and you will then have it at about its max IMO.