Performance wise, the i7-720QM has a little bit better than i7-620M.
Here the comparison:

i7-720QM:
1. Faster memory bus (DDR3-1333)
2. 6MB L3 Cache
3. Clock: 1.6 up to 2.8Ghz

i7-620M:
1. Memory bus (DDR3-1066)
2. 4MB L3 Cache.
3. Clock: 2.66 up to 3.33Ghz

Here come the drawbacks:
1. Due to higher TDP in i7-720QM, battery performance doesnt do well with this processor rather than i7-620M.
2. Due to higher TDP in i7-720QM, i7-720QM have high temperature than i7-620M.
Verdict: Its all depending on your task and usage. If you think you can fully utilize the quad core, go for i7-720QM.

is the error only saying this value: 0x000000 ?
because you can check the cause from these hex code meaning:
http://www.easydesksoftware.com/stoperrors.htm

not sure what the cause, did you do something? like install something e.g: driver etc.
system restore do works in this case if you unable to figure the cause..

update your AV and run full scan.
and download MalwareByte (if dont have any malware scanner), update, and run it too.

if you interested, you might want to read this:
http://forum.notebookreview.com/hardware-c...-fast-ssds.html

Guys, how to make my Z image is smooth? When I view Sony Style USA website, the images seems jagged. So, what can I do to make its smooth and quality without blur or jagged pictures?