Tren reduces IgF1 levels, I would think by its activities in the liver, but sensitizes IgF1 receptors in skeletal muscle.
I think you are correct in that comparing different GH products at same dose, with and without tren in the cycle, will not result in meaningful conclusions about GH quality. One would need to run and test both with same accompanying anabolics to identify any real difference.
My guess is that igf1 levels would be nearly the same between various Opti kits at same iu/day schedule, with anabolics held constant. Opti and other good generic GH these days test well with very high purity and minimal if any dimer - not particularly confident most Pharma GH would test as well. That’s not to say Pharma isn’t as good, as manufacturing techniques, excipients, storage are all relevant to end product quality.