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The Asrock has little better voltage controls than the MSI and can reuse your old 775 HSF. Also has ESATA port. Unless the Asrock different features appeal to you, I'd get the MSI for a budget build from your choices available.
MC deal got me into this bundle. Very easy install on boot on SSD via Win7 on usb and Asrock now has a 3 year warranty so no worries. OC with UEFI bios is monkey-see easy. Get the MC deal while it lasts.
Also if you have a non-stock cooler for your AMD setup that will also fit 775 boards...
I'd get an 6870 or 560GTX both around 150-160 after MIR or you could get a 6850 for 130 after MIR and OC if needed. Spending alot more probably doesn't do you much good good given your CPU.
You can certainly leave it connected while you are using the computer but I wouldn't leave the 2.5 drive running 24/7. You don't have a fan in a drive that small and I'd be concerned about higher temps decreasing the life of the HD.
found a cool prog HDDScan for HD info http://hddguru.com/content/en/software/2006.01.22-HDDScan/ it can read SMART info and map sectors that have high access times. See if the consistent dips in your HD-Tach graph correspond with areas with weak sectors. There are also progs to turn weak...