Sorry I can't really compare to a Silver as I've never had one (though I suspect growth rates wouldn't be drastically different esp. when younger), perhaps others will weigh in.
But for Asians in my personal experience it can be 1/2" to 1" per month. Of course factors such as caloric intake, amount of exercise and also tank size can affect growth rate -- generally the bigger the tank the faster an Arowana (like many monster fish) will grow.
Btw, I would personally try to get the fish off of feeders and onto pellets and fresh or frozen foods (at that size frozen ghost shrimp are a great option) soon as you could -- the longer you wait the harder it will often be to get them off of live foods.