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.
I've scoured the net to find some reviews from ppl that have demoed the board...so far both sound pretty solid. Thanks for the website, can never have too much information