Will you be paying $500 or so for a 3% performance difference?
Will you wind up with a dead 820-2850 that randomly kernel panics for no reason, with no recourse other than to curse at the expenditure you put into this machine? Absolutely!
Apple used to fix these under an extended warranty program that remained silent for a long time; it is expired. See here. https://support.apple.com/en-is/HT203554
This board is, by definition, from the manufacturer itself, a piece of crap. If you spend $500 or so sourcing a replacement board for your laptop, it will most likely be a board from another randomly kernel panicking computer, you will be stuck with it, and it will all end in a nightmare mess. :-(