I've noticed that I have been able to increase my effective backpack/inventory space by receiving quest rewards and never selling weapons/items. If you get an item from a quest when you have a full backpack, you go from 27/27 to 28/27. Since backpack space+bank space are annoyingly small to me, I've been using/abusing this feature to get a backpack space of more like 36/27 or more. Is there a limit to how far that I can take this? I haven't noticed any downsides; I just swap weapons from my hands to the one on the ground if I want to pick one up (this doesn't increase the number of things I'm carrying, it just allows me to still acquire loot by trading it with the stuff in my backpack). Is there an upper limit to the backpack size with this technique, or can I effectively increase my backpack space ad infinitum?
For reference, my current backpack size looks like this:
I now have a backpack size of approximately 150/27, and am not experiencing any difficulties, aside from occasional issues when trying to trade with other players (I seem to have to give as many items as I receive, or the other player's game complains that my backpack is full).