I stacked 4mOhm on all 6. The 3mOhm figure was just my estimation of how much resistance is added from the silver paint at the joints.I'm a little confused on which ones you used on the card, did you just put 3mOhm on all 6?
Edit - what if I don't want the card to pull an insane amount of power, I would like to just increase it to maybe 500w, should I stack all of them or just some and which mohm would I use?
If you are looking for a 500w limit, I would bridge across the top of all 6 resistors using the MG Chemicals 842 silver paint (paint only, no stacked resistors). This will process will give you somewhere between 500w-525w max power limit if done correctly. There is more information on this further back in the thread.