So basically it was suggested to use the damage Quicksilver done instead of the KE of him. In this case I'll be using the KE of Cap falling backwards instead of the KE of Quicksilver punching him. Feat can be seen here.
Peak human discus throws are 82 mph, or 36.65728 m/s. It seems to be moving but it's not, it's just the camera panning. Assuming snail speed or 0.001 m/s, which is suggested on the Calculations page (my previous calc says 0.05 m/s, but looking back it seems to be a random number with no evidence).
36.65728/0.001 = 36 657.28x time dilation
Quicksilver punches him in the head. Even in time dilation his hand is a blur. According to our Speed page if it is not visible to the human eye it is subsonic, but just to be safe I'll use Superhuman speed, which is 12.51 m/s minimum.
We can calculate Quicksilver's punching speed here
36657.28*12.51 = 458582.5728 m/s, Mach 1347.62
The linear momentum of Quicksilver's fist and Captain America needs to remain the same.
FinalSpeed = (MassQS*InitialSpeed):(MassCap+MassQS)
Hand+Forearm is 2.23% of human weight. Aaron Taylor-Johnson weighs 70 kg. Therefore 1.561 kg. Cap is said to be 240 pounds, or 108.862 kg.
(1.561*12.51):(108.862+1.561) = 0.18 m/s
But this is dilated time.
0.18*36657.28 = 6598.3104 m/s
0.5*108.862*6598.3104^2 = 2.36980055603e9 Joules, 566.40 kg of TNT, Building level
I'll calculate Hawkeye's durability when Quicksilver ran into him in the beginning of the film as well, just to know if it would result in any upgrades. It's at the start of the video I linked above.
In that scene Quicksilver was fast enough to dodge Hawkeye's arrows effortlessly. Hawkeye’s bow is the Hoyt Gamemaster II, which has a draw weight of 35-65 lbs (I'll take average of 50). An arrow weighs around 0.0227 kg. The distance Hawkeye pulled the bowstring was 2 feet.
100 foot-pounds, or 135.582 Joules. sqrt(135.582*2/0.0227) = 109.3 m/s. Hawkeye's arrows are 109.3 m/s, which makes sense. (I am aware that getting speed from KE is usually not allowed, but this is a real-world bow so I figured out it would be fine).
Aaron Taylor-Johnson is 70 kg. Jeremy Renner is 82 kg.
(70*109.3):(70+82) = 50.34 m/s
0.5*82*50.34^2 = 103 898.7396 Joules, Wall level
Nope, no upgrade.