Hi Sir,
We have done the presure test on the NIC with based on Fedora server 22 for more than 48 hours, it is stable enough to provide bandwidth about 95MB/s.
May I know what storage device you were using for downloading? Maybe there is something wrong with the disk when sequential write and read?
BTW, ubuntu server 14.04.3 or later version is working fine on Jaguarboard.