If you ever want decent reviews, not just random ones from people who haven't even ridden the board but like the graphics, check out shayboarder.com. I haven't demoed either board so I'm going off the research I've done while looking for my own setup. If I'm remembering correctly there isn't a '10-'11 review on either of these boards
Keep in mind that from the 2009 to 2010 model for the K2 Eco Pop, K2 changed from zero camber flatline to a rocker. I believe the NS Infinity didn't change except for the graphics so the 09-10 shayboarder review will be pretty on point.