Keep in mind for your i5 build you can go with the P7P55D-E Pro for ~$180 and save ~$60. There really isn't much difference between the two other than an extra network port, sata slot and some other small stuff. The main functionality is the same and you're probably not going to utilize all the extra stuff you're paying for.
Also if you go with the i7, you should really use a triple channel ram kit, since it will be the LGA 1366 socket, which would be around $150. Not the $100 you estimated.
If you're buying from Microcenter, the i5-760 is only $170. This means the i5 build you listed should be about $505 and the i7 build should be $610. Throw in $24 to both builds if you plan to overclock and grab the CM Hyper 212+ at microcenter.
You can grab the Samsung Spinpoint F3 1TB for about $60 at microcenter or with the promo on newegg. It's faster and higher capacity than the WB black you listed.
I would go with the i5 unless you plan on doing some intensive video encoding or some Photoshop/CAD work. The i5 is excellent for gaming and gaming PCs are usually plenty good for everything else. Unless there is a sudden shift in computing technology, either build should last a good 5 years or more.
Basically it all comes down to if you want to pay the $100 for hyperthreading or not. HT may be useful, but not so much to the average PC user. If you aren't using those extra threads now, chances are you're not likely to use them much in the future either. Especially when upgrading from 2 core to 4 core.