Good videos Blueberry.
I have little experience pruning peaches to a central leader, so I won't comment on that. I more or less prune the way the extension agent in the video does, with a few exceptions.
First, as Alan mentions, I start my scaffolds pretty low. I've started trees with higher scaffolds and it's harder to keep those trees as low. I also tie selected scaffolds fairly close to horizontal. This produces a scaffold nearly horizontal for the first few feet, then it turns more upward, where it wasn't tied down.
As the tree grows I adjust where I want the growth to be by way of pruning. The new scaffold which turns upward will of course send out all kinds of shoots. One can simply choose which shoots to keep as extensions of scaffolds, and which to prune off. If the growth is too low, that growth will eventually be pruned. If it's too tall, that too can be pruned off.
The weight of the fruit will pull the scaffold down some, but for the most part it bounces back after harvest (I'm referring to the scaffold, not the individual fruiting shoots.)
I prefer the almost horizontal angle of the scaffold as it leaves the tree. I think it produces very strong crotch angles w/ no risk of bark inclusions. It may be that Alan and I have discussed the strongest crotch angles in the past (it's a bit fuzzy since we've had thousands of forum conversations over the years). I don't recall if we ever came to a consensus on this.
I also try to prune somewhat narrow crotch angles which come off the scaffolds. I think it's easy for people to neglect this. In other words I think there is a tendency for people to think they are home free once they get rid of narrow crotch angles for the scaffolds (where it attaches at the trunk) but I've found any narrow angle on the tree is subject to breakage (at least in our high winds).
Drew's question is a good one about how to keep a tree within 8'. The difficulty in understanding is found in the assumption of how peach trees grow. The question assumes peach trees only grow at the top point where the last growth left off, however this assumption is not correct. A properly pruned peach tree will put new growth all along it's scaffold (i.e. down low and clear up at the top). The very top growth will have to be removed to keep the tree at 8', but there will be plenty of growth lower down, if the tree is maintained properly.
That's why it is so important to keep lots of light in a peach tree. A densely packed peach tree is a death sentence to all the lower growth. Apple shoots will tolerate some shade, peaches won't. My peach trees are fairly vigorous, so it is critical I prune at least twice a year to keep them open (although very young trees may only get one pruning per year).
I don't crop my trees as heavily as the extension agent in the video. He mentioned an 18" shoot could fruit 4 peaches. I would only leave two fruit on an 18" shoot. This produces bigger peaches, but less overall weight on the scaffolds, so the scaffolds pull down less. I've fruited with the kind of density the extension man suggested, but it causes me too many problems. First, unless the variety of peach naturally produces really large peaches, the peaches will be pretty small at that density. Secondly, there is just too much weight on the scaffolds. I've propped up scaffolds to keep them from breaking in the wind because of too much fruit, and it's a pain. I don't have time for that.
I also don't trim back shoots to strengthen them as the extension agent suggested. This may also be related to how many fruit the shoot is allowed to carry. With less fruit, there is not undue force on the shoot.
There is quite a bit of difference in cultivars regarding how upright the peach tree wants to grow. Some varieties want to grow straight up and you really have to work harder earlier to keep them low. Some are more naturally spreading (like Redhaven, Harrow Beauty, etc) and those trees are easy to manage and can be allowed a little more leeway on their upward growth. Regularity of fruiting also plays a role. A tree which is more hit and miss won't have the fruit to pull it down, and so requires more aggressive pruning to keep it from going up. Donut peaches also want to grow straight up, since they don't have the weight to pull the branches down. Years where all the peaches are frosted off require more heavy and frequent pruning to keep them low.
Peaches don't send out new shoots from blind wood, as readily as other fruit trees. Because of this, if I want renewal wood at a place on the tree I will leave a stub cut (called a hat rack) which will throw out new wood.
That's about all I can think of. Starting to ramble here.