I just upgraded my 2012 GT500 convertible, your excellent videos made it pretty easy.
I used 2 pairs of Kenwood KFC-P680C speakers in the front and back, and the Kicker subs from Shelby American. The Kenwoods were $90 a pair from Amazon.com, and the Kickers were $150 from shelbystore.com. I also got 2 Metra 72-5600 adapters for a total of $15. The total was under $400 for everything including shipping and tax.
I also bought the Boom Mat foam speaker baffles, it turned out there wasn't room for them so I didn't use them.
If you get these speakers, you're going to need additional 3/4 inch long #8 self tapping screws. The OEM Ford screws won't work on the Kenwood speakers, they have a shoulder flange that's too big. Kenwood gives you 6 of these per speaker pair, but you're going to need 14 per pair total: 4 to secure the plate, and 3 to secure the speaker to the plate. So buy 20 of them just in case. Luckily I had them in one of those assortment packs so I didn't need to go to the hardware store.
Following the videos it was pretty easy. Working at a leisurely pace the driver's side took me about 2 hours to do the front and rear, and the passenger side about 1 hour.
The sound improvement is unbelievable. I did some fairly critical listening to the OEM speakers playing Steely Dan's Gauchos, and Aimee Mann's Charmers. The Kenwood/Kicker combination has much more extended highs - such that I can still hear - and a smoother midrange. Vocals are noticeably clearer. The bass doesn't have a one note thump like the OEM speakers did, drum sounds are more clearly defined.
I know a lot of people have sprung for big amps, and if you're going to really have a great system of course they're worthwhile. But I have to say that the Kenwood/Kickers seem to be more efficient than the OEM Ford, and they will definitely play louder. I don't feel like an amp is required at all.
This is a great upgrade, well worthwhile, and it's what I would highly recommend unless you're going to spend a lot more money.