Nice looking stick you have there, would be pure joy with 18-20" fish!
OPST are spot on with there recommendations but I suspect there will always be a grain window influenced by many factors. I asked for a match for my ACR 1175 and was told 300gr. Well yesterday I thought I would try their 250gr ( 225 and 250 which I have for SH rods) with 10' type 3 versi leader. It felt way to light rigging it up, but cast beautifully with a nice crisp off the tip cast from the 1175 on the river, even managed a nice little brown from the town water I was swinging. Gary's rods are a nice smooth casting tools and I imagine yours is no different so if your happy with the lighter gr weight not much will be achieved unless bigger tips are required to be cast.