i have a gx620 desktop (large model, not sff, not mini tower) and was looking for a replacement cpu. however, the computer does not support core 2 duo. i also heard that the optiplex 755 motherboard will fit in a gx620 case. is this true? if it is, will the motherboard use the same cooling? and will it support core 2 quad, or just duo? also, does it support the same pci-e riser?