Well if it's avoiding the realm's taxes you're wondering about, I think taxes are set to greater than, not greater than or equal to, and it counts the separate values of gold and bonds, and taxes one of them that overflows, rather than the total. I could be wrong on this though.
What does this mean? Let's say your realm has a 25% tax on anything over 100 gold. Theoretically that would mean you would have at most either 100 gold or 100 bonds. I think, but I've never actually made my own attempt, just looked at the Information\Check Taxes screen, that if you have 200 gold and split it 100 gold and 100 bonds, you don't get taxed.
