Once you've replaced the network cables, you're not going to see any significant improvement because of the poor write speeds on your disk array. Not to say that there wasn't a network cable problem there, but it is not the only problem.
I'm not very familiar with highpoint products, but you should check out if there is a management software for the RAID controller. Check to see if there are any problems reported from any of the drives, check write cache settings, etc. You might also check windows event viewer and see if it is throwing any errors accessing the RAID disks.
The card he lists has a max 4k strip write speed of 150MBps and hitting 450MBps using a 16K stripe. Those cards are by far not "cheap crap consumer" level. Not "ultrahigh level server" but decent over all.