I had 3000's and my feet used to cramp up within 5mins, I tried thinner socks to the point that they felt like they'd fall off and it was still the same, my feet just didn't like them. Then I got some Ice with the Millenium foot pockets which were much better, but I have to use 5mm sock on one foot and 3mm on the other to be sure of no pain.
Its just a case of finding what suits your feet, you'll know when you do
