There was something somewhere but just to state a few temps (ones I know),...
At room temp (this is 75F, NOT 68F), about 21-22PPM max.
At 150F, about 40PPM.
Silver oxide is not overly soluble in water. I don't know what it is at a higher temp but I doubt from 150F to 200F you'd be up even as high as 60PPM.
From what I've heard, most people who manufacture higher PPM Colloidal Silver here run around 150-160F. Thats hot enough that adding the reducer at the beginning of the run for the total PPM you're making (plus a little extra for "insurance"), reduction can keep ahead of production fast enough that you never exceed the solubility limit in this temperature range which is all you're really looking for.
Running at 10ma, it takes 30 minutes to pull 20mg of silver into solution (that'd be a liter of 20PPM). At 150F, you can get to 40PPM before you have issues so thats a whole hour. For sure the reducer is going to do its job much more quickly than you're producing... As long as your rate of reduction outpaces your rate of production, you can basically go as high as you want in PPM - for sure 320PPM which a lot of guys here make. Processing cold, you will most likely run into issues just so its said.