Upper limit of SD card ports throughput

Hi Nikolaus!

I am wondering SD card of which speed (and price) makes sense with Pyra. In other words, which speed can be utilized and is not a waste of money. I believe hundreds of backers are interested in this, too. So this info should be published on Pyra Wiki in comprehensive form. Asked on IRC, but didn't get any solid data references. Most credible comment was aTc's "it all depends on how hns has the sd slots connected anyway". So I am asking you :)