I see things a little differently than others. Sometimes this leads to helpful solutions. Occasionally I manage to over complicate things. Regardless I always try to be open to other viewpoints.
You may need the most recent BIOS update but the T420s supports 16GB of RAM, not 8 as previously (and correctly at the time) published. You can use RAM that is faster than 1333 MHz, but it will not use a faster speed than 1333 MHz.