Yes, you should use the 60gb MBR. The MBR contains the partition layout, so you want one that matches the size of the disk.
Regarding the two firmware files, they are in fact the same firmware (if you download both and compare the Firmware-X.Y.Z files, you will see that they are byte-for-byte identical), so it doesn't matter which one you download. I've no idea why there are two different versions.