Core i5 is your better option. You are not going to need an Xeon X3000 processor because the only difference between that and the desktop CPUs is that it has support for registered and ECC memory. Using Registered/buffered ECC memory in a desktop is pretty pointless. Only in a server which answers multiple requests and is mission critical would these features be used.
So just get a "Desktop CPU" (Athlon II, Phenom II, Core i3, i5, i7). Manufacturers will try to sell a Xeon to use as a workstation CPU while there is really no difference, at least one that matters for your application.