Just to be clear: In twenty five years as a biologist and six years getting various degrees in biology, I have never engaged in a discussion of what was THE top predator, or even A top predator in any system anywhere, nor have I ever heard any biologist say that there was one. The reason for this is that it is recognized that there isn't such a thing as a top predator. The concept top predator is used to cover a variety of species in any system, whether a large system like the ocean or a micro system like an individual coral reef. The members of that group are never clearly identified, as it is well understood that there is no such thing. Every animal (with one partial exception) ends up passing through the digestive tract of a different animal. The partial exception is that some humans are cremated such that the bulk of their body mass at the time of death is liberated as a gas and is not eaten by anything.

The reason I talk about Orcas in this thread is only to show the fallacy of your attempt to find a single pelagic predator that can be considered a top predator. However, you reject every bit of evidence presented that is counter to your views, and you present no sound evidence to support your conclusion. You have started with the assumption that animals are designed for a purpose, and consistently attribute human characteristics and motivations to various other species, yet you provide no evidence to support those attributions. As an armchair exercise, figuring out which animal is tougher than which other animal, is entertaining. The danger is that you will actually believe your conclusions have any validity. This failure results in phyisicst who long asserted that bumblebees couldn't possible fly and that rising fast balls were impossible. They had models that showed these things were impossible, and they asserted that their models were correct, sometimes even past the point where video evidence proved that they were wrong. In your case, even video evidence won't convince you.

However, I did some of the work for you. Here are some papers on orca predation on mako sharks (and other things). As the first paper notes, there is little direct evidence of orcas preying on makos. However, there are dozens of papers on orca predation on Google Scholar, alone. Naturally, the citation list, and a study of papers that cite these papers, might lead you to better data. Interestingly, while there are dozens of papers on orca predation, including some that list predation on makos, there are relatively few papers on mako predation, and I was unable to find any that showed even a single instance of makos eating orcas. My investigation was trivial, as I have little interest in it, but the results are still suggestive.

This one is pretty awesome, if you read it, because a diver entered the water to get a better look at the orca attacking the mako. That takes balls of brass.
http://aquaticmammalsjournal.org/sha...03_Berghan.pdf

Not makos, but still interesting:
http://www.sharkmans-world.eu/research/killer_whale.pdf

Note Table 1, which lists makos as a documented prey species. One point about this paper is that it directly refutes your claim that the teeth of an orca are not adequate for eating sharks:
http://www.orcaresearch.org/wp-conte...rhead-orca.pdf

While not conclusive, this suggests that your makos rarely eat other sharks, let alone anything larger:
http://www.springerlink.com/content/utm52r0g4416v954/

This ones pretty cool to a biologist, since it considers both the trophic cascade and trophic fountain, which most people ignore in favor of simpler theories. It's pretty much a constant annoyance to me, but leave that aside. Once again, it has nothing to do with mako predation on orcas, but I haven't found any evidence that that happens....EVER! A couple points that you might take from this paper: Makos eat lots of squid, and there is yet another micro-refuge that you didn't consider. You evaluated whether a species could out dive another to get away from it, but you didn't consider whether they differ in their hypoxia tolerance. This paper suggests that you should consider that, as well:
http://fishocean.info/jumbo_squid_mako.pdf

In summary: Makos don't eat orcas, but orcas eat makos. Therefore, the mako is lower in the food chain than the orca, despite your models that suggest otherwise. Interestingly, in the first paper, the mako clearly is not attempting to use its superior speed to avoid the orca. Instead, it attempts to hide under a structure (the diver, at first, then the boat) rather than simply run away. So, at leat in one case, the mako is not using the strategy that you expected them to use.