the i7 is better but only if you were going to use it to it's full potential. %99.99 percent of games aren't going to use the extra threads that is has. so only if you're going to be using programs with hyperthreading support should you get the i7. otherwise go with the i5-750 and the Radeon 5870.
If you live near a microcenter you should consider going there to get the i7 930 which is on sale for $200 and has been for some time. If you are going to go with an i7 I would thensuggest getting the Gigabyte UDR3: