I would say, for most people unless they're using some pretty high GH dose; genetics will probably determine who will get up to that level. Some people's levels are more elevated before, and after the use of GH/peptides. That's why you see so much variability in serum/igf tests; it's all about individual physiology.
Similar to how one guy can be at 1000 ngl of test on 100 mgs of testosterone, and some need to go as high as 200+ to achieve that level.
In contrast. It's theorized, in-controlled settings using human peripheral blood mononuclear cells (in-vitro) given supraphyiological doses of GH/IGF-1 could potentially disrupt mitochondrial function via oxidative damage.
Highest I've ever had was a 655 last February while using 6iu/day TP's black tops. This was the highest test I've ever had and I've had IGF tested 50+ times over the years while using all different kinds of GH- both generic (including the old Rips) and US Pharm Grade (Mini-Quicks, Omnatrope).