As far as future games, I don't have a crystal ball as to what future games will or will not require. At this point in time, there's nothing to indicate a multitude of games will arrive running on 8 cores. It's strictly a budgetary decision. Yes, the i7 is a better gaming CPU then the i5, that's indisputable. You will see an extra 3 - 6% out of an i7 than an i5.....1) they are clocked higher and 2), they tend to overclock better.
Drop the sound card save $30 and invest $15 in a better case.
$80 - Corsair 500R
http://www.newegg.com/Product/Product.aspx?Item=N82E16811139010
Save another $48 with the MSI 780 - $465 - 5% off w/ promo code JUNECLEAN3, ends 6/30 - $30 MIR
$412...