if you are interested in moving air there is only 1 stat that you should be interested in and thats CFM. In short the higher that number the more air is being moved. The only problem with that however is the higher the CFM the louder the noise.
1 question though, most case fans that I’ve seen are 60mm and up. Where are you finding these extremely small fans?
personally I use these http://www.vantecusa.com/p_td_8038h.html
so if you change your mind and want a 80 or 92 you can go for these. But something that small I’m not sure what you’ll find