A few things regarding Japanese version.
Damage boosting in US from fire/leaf to big costs 32 frames. Getting powerup from big to fire/leaf costs 32 frames.
Damage boosting in JP from fire/leaf to small costs 48 frames. Getting mushroom costs 48 frames, then fire/leaf costs 32 frames.
Therefore, each damage boost in JP costs 64 frames more than in US, plus the slowdown required.
The P wing route:
The glitched item in 5-1 can ~~only~~ be obtained using a P wing. After that is 5-F1. First, you have to get rid of the tail so there's 48+48+32=128 frames plus slowdown. There is no fire flower in 5-2 or 5-F1. 5 seconds lost as you cannot firekill Boom Boom. These are not accounted in Mitch's video.
A quick glance, the fastest powerups to get is the 4th mushroom in 5-5 and the flower in 5-7. Though inability to firekill the red koopa troopa in the way forces a star be used in 5-7. As the platforms after are infavorable to charge pspeed. Star has to be used, costing 44 frames.
In 6-F1, the fact that using a star is 1 frame short of getting through the spikes corridor, the P wing should be used. Otherwise, wait for the elevator and take damage once. IIRC it is half a second slower. But the longer damage animation should reduce the invincibility frames that have to land on the spikes much further. Or use a star and take damage.
6-F2 is ended with tail or small. The damage boost in 6-8 is not available as doing so will not get us the fire flower in 6-10. Meaning that we are playing 6-8 and the start of 6-10 as tail. In 6-8, you will have to run up the slopes, and having slighly lower than 56 throughout, and unable to get the 61 or 62 speed benefit from slopes.
Or, damage boost in 6-8, do 6-9, stomp kill in 6-F3, get mushroom and stomp kill in 6-A, a jump around the 1st Piranha. This way, I guess it loses little time.
Edit: Well Maru theorized a route keeping fire throughout W6 and is 1.9 seconds faster. So problem solved if this route is used.
Into 7-4, now there is a trouble. As a P wing is used for 5-1, we run out of P wings. We may have to switch back to cloud 7-4. But hey, we can cloud 6-F2 to save the P wing for 7-4 and get the mushroom in 6-8 and having faster 6-8 but it still uses a cloud which
DEFEATS THE WHOLE POINT OF GETTING A CLOUD IN 5-1!! There are limited P wings for TAS and trading a cloud with a P wing is not viable.
Therefore, the leaf route:
There are 2 leafs in 5-1, both at the beginning. P speed isn't available. Though in comparision to P wing with little ground it isn't much slower. In the end, I believe P speed can be charged before entering the pipe. After reaching the top, not having P speed is faster. Still, 5-1 as a whole would be slower. However, unable to firekill Boom Boom in 5-F1 and powering back up before 5-F2 still holds true.
After 7-F1, you would be either tail or small. Small means you cannot clip 7-6 (although you can wall jump). Tail means you cannot clip 7-7 as there is not enough room to accelerate. That means tail has to be kept and 7-8 is played instead, which is slower than 7-7. 7-8 is either played without P speed, or damage boost, and then get the mushroom in 7-9 to do the clips. Both options costing a lot of extra time.
Get the fire flower in 7-A and the rest is the same. So where to use the extra cloud? Probably to resolve one of the problems mentioned above. It wouldn't get the largest timesave possible, but makes a JP TAS with minimal P wings possible. The most suitable candidate is 6-F2, clearing which is 30 seconds. And it actually ends up the same with the P wing route.
In RTA, 7-4 must be clouded. 2 out of 3 levels between 7-9, 7-F2 and 8-F are played. In TAS, cloud from 7-4 can be saved. 7-F2 and 8-F both are clouded. 7-9 is clipped with ease. 7-4 and 7-9 both become short levels. The next long level clouded isn't really long. So the benefit would be less than Mitch using 8-F for the calculation.
Lastly, music box is not obtained from 5-1. To choose between fighting 5-HB and 7-plant, HB with the P wing should be fought. There is extra 10 seconds.
The TAS route is different from the RTA route. Which items to use, in-level routes, etc. are different. While JP
might be faster for RTA, it doesn't mean it is in TAS. Damage boosting being from leaf to small brings up a lot of problems more than the literal 64 frame animation cost. Extra P wings have to be consumed. All and all, the route would be reverted back to be similar to the second to last published movie
[3028] NES Super Mario Bros. 3 "warpless" by Lord_Tom & Tompa in 46:20.30.