Check that the RAM is 1.5 volt . Sandy bridge processors need that You dont say what your usage is but if its primarily gaming then you dont need more than 4 gig . T
You also dont need a 620 watt psu . A good 450 watt unit should be fine , but at that price its good value
I would buy a 22 inch monitor , meeting the extra cost with money you save on RAM, and if necessary a slightly cheaper case .
After all you spend your time looking at the monitor , not the case