Optimal hammer weight for 18 inch barrel?

I recently picked up an 18 inch .22 barrel, and was hoping to hit 900 fps with Polymags. As it turns out, I was getting about 860 fps with the wheel cranked. So, I added a hammer weight made out of a bronze bearing and two bronze washers, increasing the weight by about 30 grams. This brings the total weight up to 80 grams, and I am now hitting 905 fps with the Preds and no turns on the power wheel. While I am happy with the results, I am wondering if this is going to be hitting the valve too hard and possibly doing damage. Should I try messing around with the weight some more and maybe just tweak the adjuster a bit, or will it be okay with this much weight?
Thanks,
Chris