Hi Turtle, some few suggestions from the videos:
Against Gief: tostada splash/propeller/fajita buster can be dangerous to use against Gief since if the Gief does the backdash correctly on time, he can do SPD right away while you're recovering from the whiffed move.
Of course, this only works if the Gief knows about it.
I find that Fuerte's jumping fierce is an excellent tool to keep a lock down on Gief - it takes care of backdashers and recovers fast enough for you to do another move if blocked.
And yes, Fuerte's jumping fierce beats all of Gief's options on wake up besides FA to dashing away. Just make sure you hit it earlier than with other characters since Gief has a huge hitbox - you can get hit by wake-up lariat if you hit it late.
Against Boxer: i would suggest not to use too many wall-jumps to splash since a boxer who's used to it will just do headbutt that will either trade or beat the splash.
A normal move I've started using against boxer is the far s.HK.
You cannot really use this move to anticipate a dash punch but you can throw it randomly since it sometimes hit boxers doing dash punches. And if it's whiffed, you have enough recovery time to block and sometimes even do a run back to tortilla propeller/splash.
One useful random application of far s.HK is that it hits armored dash punches twice for a whopping damage of 210 and a good stun.
Far s.HK beats all armor dash punches, TAP, and overhead. It basically beats all of the slower dash punches (which usually armor breaks). Fuerte's FA will take care of the fast dash punches since none of them are armor breaking.
Other use of this move is to slowly move Fuerte close to a turtling boxer without using the run. Far s.HK moves Fuerte a bit forward so you can catch a turtling boxer by surprise by doing a quick run to splash.
Ambigious cross up jumping fierce on wake up can be pretty useful since it will whiff headbutts and I think you can try to do a quick guacamole throw on a whiff headbutt.
And if Boxer tries to do a TAP to escape the cross up, sometimes it will end up facing you where you get a free throw to punish it.