If you can afford spending 200-300 on a mobo and 70-120 on RAM then go i7. You can sell your current rig to make up for the price.
I sold my E8400 rig minus the hard drive and case for $450 to a friend of mine (Corsair 620HX, 8800GT, Gigabyte P45 mobo, GSkill D9 RAM, etc...) and bought stuff (...