Not to play Devil's Advocate (no pun intended), but I believe that I will have to (respectfully) disagree with you and the previous answerers.
As you and I had done earlier, we should examine Godel's Incompleteness Theorem. A quick (and poor) hashing of it would simply be that 'there is no self-sufficient sub-system that may function solely on its own truth'. Or, worded more plainly, everything has a higher truth above it. Naturally, this begs to question what that truth is. Atheists say the infinite characteristics of the universe. Theologians say God. What we choose to call it really doesn't matter, as long as we recognize that there is an initial truth that kick-started everything else.
That being said, we may state that we now DO have a system (note that this is THE system, not a sub-system) that is self sufficient and that operates within itself.
We must now also recognize that we are sub-sets of this system. That we, being minor systems within this larger one, must adhere to and operate under, the same guiding principles that the larger has set forth.
Therefore, we know that we operate under the truth of the larger, that what the larger follows, we follow. SHOULD we begin to operate under the same conditions that led to this truth (NOT what the truth follows, as that would be a paradox), we find that we COULD reach our limit, which is THE truth. So, we do have a limit of understanding. It just happens that that limit is God (or the Infinite Universe, whichever you choose to view).
But you aren't mentioning Godel or any of this jargon with higher truths, you're discussing ideas of individual knowledge of and its purity.
When we are looking at epistemology, its hard for names like Locke and Hume (and Descartes and Feyerabend, but that's another story) NOT to come up. After all, Hume was really one of the first to thoroughly ask "just what do you truly know?". And I agree with him (at some points), but to his ideas do have error. His philosophy operates under the assumption that we have two separate bodies exchanging information through sensory. However, his ideas fail when we examine something that does not provide sensory. Currently, the only two (I generally consider them to be the same, but that's just me) examples I can think of are logic and math. We defined logic. We defined math. Does that mean that we are susceptible to Godel, as well? Yes (and no). Math is an evolving subject. Its both rigid and flexible. We had pre-Euclidean geometry, then Euclidean Geometry, then Riemann based, etc. So, each "era" of math is very susceptible to Godel's theorem, but the one following it debunks the previous "higher truth". It's only a matter of time until we evolve to our limit.
Haha and, as Calculus bears witness to, we may infinitesimally approach that limit. We may get that difference down to zero.
Sorry if my thoughts were convoluted or hard to follow (I didn't have much time to frame my ideas).
Feel free to email me with more Theology questions (truth be told, I find discussing them entertaining).
P.S. Check out Paul Feyerabend. Very unique ideas. (Oh! I also feel that Hobbes was more correct than Locke, but that's just me).