Your post got me thinking on a completely different tangent: How much of the filter might be at a high tech level for most species but we managed to escape it based on what resources we actually lacked?
The most obvious example is the amount of U-235. If humans had arose 2 billion years ago there would be about six times as much U-235 on the planet (since U-235 has a half-like of around 700 million years), making it much easier to develop nuclear weapons. That could have a substantial negative impact on a species chance of not wiping themselves out.
I'm not sure how much this would matter in that fission weapons are a lot easier already to produce than fusion weapons. Moreover, this would also make it easier to use nuclear power for productive purposes. Even a Fermi style pile would be much, much easier to construct (Fermi's original pile did not use enriched uranium). So the ability to use nuclear power in this way would help for simple electricity generation a lot as well as nuclear rockets (which would directly help beating the Great Filter). So overall this seems like a wash without a lot more data.
Is there some other isotope that could have a similar impact? Possibly something that now is very rare so we aren't paying much attention to it? The other obvious candidates don't seem to work. For example, tritium has a very short half life but natural processes produce more of it so that shouldn't matter. Similarly, plutonium 239 has much too short a half-life so that any species that arose even after the first billion years wouldn't see any substantial amounts of it. Maybe Plutonium-244? It is primordial, has a half-life around 80 million years, so would be around in larger quantities on a young planet. But I don't know of any obvious fission chain for it, and the quantities produced would be very little, since it is not easily produced in supernovae.
Most accessible nuclear power on our planet isn't stored as U-235 anyway. We can get a lot more by converting uranium into plutonium, which is heavily restricted because of how much easier it is to make weapons out of, or out of thorium, which is safer and more abundant but requires a different procedure to extract energy which has never been developed for commercial applications.
One serious issue for evaluating existential risk is working out whether most of the Great Filter is behind us or in front of us. This relates to the Drake Equation and similar attempts to estimate the frequency of life in an obvious way.
Over the last few years, it has become increasingly apparent that extrasolar planets are common. However, what fraction of these planets lie in their stars habitable zone has still been an open question, primarily because most of our current methods for planet finding easily find planets that are either very large or are very close to their star (ideally both).
A new study, using the data from the Kepler spacecraft, estimates that about a third of all stars similar to the sun have at least one planet in the habitable zone. There are some issues with this estimate, and Phil Plait discusses them at his blog. The estimate has a large amount of variance. The paper actually estimates 34% +/- 14% and the issues that Phil brings up increases the uncertainty in both directions but it seems safe at this point to consider this not being very far off.
One obvious issue from a Fermi perspective is that some systems will likely have multiple planets in this zone. Also, having planets in the habitable zone is clearly not sufficient for life. By the standard estimates for habitable zones, Venus and Mars are both in the habitable zone of the sun. And there may very well be ways for life to arise outside the habitable zone. Moons like Europa and Titan seem to be excellent candidates, and we can't rule out more exotic forms of life in other habitats although that seems not too likely right now.
However, one thing this makes clear: The part of the Great Filter that is behind us that is due to planets not lying inside the habitable zone is small. So the question is, what does this mean for our estimates of how much of the Filter is behind us and how much is in front of us?