Does dual core help transfer speeds?
That definitely doesn't make sense.  Unless they somehow turned off one core (probably impossible without serious development effort) and compared the transfer rate to when both cores were on, you can't draw that conclusion.  One phone might have a different transfer rate that another, but it has nothing to do with whether one phone has a dual-core processor or not.  The speed of the internal memory or SD card and the filesystem are the most important factors, and possibly the efficiency of the storage-handling code. All three can vary between devices.