i think the universal consensus among ALL arima owners is: weight forward. everything you can take from the stern, and everything you can add to the bow, seems to help the overall experience. speaking for myself, i've had enough weight overall to strain the outboard, but i've never had too much weight distributed forward. in my case, shifting the weight forward makes ALL the dynamics better (bouncing, tracking, turning, following seas, head-on seas), so i'm working on a belly tank conversion next. i'm actually curious if somebody has found the "too much" point, but i really don't think i've heard someone say "it was too much and i needed more weight in the stern".
that said, i would move all 'necessary' weight forward before adding ANY ballast weight. i think it's safe to say that additional weight will always lower your gas mileage (IS it safe to say that?)