You wont regret buying the FX 6300 over Athlon 250. Its way faster and will deliver better gaming, or editing etc. Plus if you go with a dual core Athlon recent games will just run on the edge and you'll need an upgrade sooner.
Asked cause when i upgraded to a faster drive the older drive became very slow. the prob was solved when i installed a 64bit OS. But in your case it seems to be some other prob.