FCAW-
If your filler metal is to match the weathering A-588; I'd go with an E81T-1W. (low 90's Ksi.).
If your filler metal is to match the A387, a 1-1/2 Chrome, 1/2 Moly pressure vessel plate, I'd use an E81T-1 B2. (high 90's Ksi).
Both are all position, (FYI-Trimark makes both).
Curious what is the joint config., and what preheat are you going to use?