Just saw the videos, you're fast but overburdening those fingers. It might be better for you long term to spread of the action to the thumb and pinkies... the way you hold your pinkies tucked high to keep out of the way seems to be a stressful position too. Do you have any pain/discomfort when you type like that for a long time?
Actually I just noticed from those videos that I actually keep my pinky tucked up high, I've never noticed it before. But thats also partially because I use my pinky for backspace and enter (Which I don't use on typeracer) so I don't have my pinky up all the time.
For pain/discomfort, I've been typing like this since I was around 12 or 13 or so, and I haven't experienced any pain/discomfort yet. Actually as you might notice, I like to keep my fingers relatively spread out and low with my arms resting on the keyboard tray. I find the normal way of keeping your wrists up and having your fingers all on the homerow to be too cramped and uncomfortable for me.
Well I also have a wierd way of using the mouse too, considering I use the mouse on the table above the keyboard tray and I position it around where you'd hold a pencil when your writing.