Hard Drive: cache and speed

1 of my 3 hard drives is failing + one drive is questionable so I'm replacing 2 of them.  I'm considering http://www.seagate.com/www/en-us/products/internal-storage/barracuda-xt-kit/ . Question is, is it worth the premium to go from 32mb to 64mb cache and from 3GB/s to 6 MB/s.  I'm not sure how to tell if my MB can take advantage of this or I'm waisting my time/$.  I'm finding them online for $180 or so.