Optimizing Resistor Values for Comparator Reference
There are several problems with your method:

If you're using 1% resistors, then you probably want that error to dominate.  That means the offset voltage due to the reference voltage impedance should be significantly less.  I'd probably aim for no more than 20% or maybe 10% of the 1% error of the resistors.  If you have four sources of error and each is 1%, then you end up with 4% overall.  You probably want to avoid that.

You are using the input bias current spec.  If you match the impedances of the two inputs, then you can use input offset current spec.

Note the rather large 7 or 9 mV (depending on your temperature range) offset voltage.  This is in addition to whatever offset is caused by the offset or bias current times the impedance.  No matter what tolerance resistors or other parts you use, it's not worth trying to reduce the error by a few 100 &micro;V when the offset voltage than adds 7 mV.

If you really care about comparison voltage accuracy at this level, then this is the wrong part to use.  7 mV is very large by today's standards.  Modern CMOS opamps also have much lower input bias currents.

Since you're using a 5 V supply, take a look at the MCP602x, for example.  You can get parts with only 250 &micro;V offset at 25&deg;C, and 2.5 mV over the full extended temperature range.  The max input bias current is only 150 pA up to 85&deg;C, more than three orders of magnitude better than the part you show.

The output impedance of a voltage divider is the parallel combination of the two resistors, not their sum as you seem to think.  You wanted 125 k&Omega; output impedance, then used 100 k&Omega; and 25 k&Omega; resistors.  The output impedance of that divider is actually 20 k&Omega;.  To get the 125 k&Omega; you were aiming for, use 625 k&Omega; and 156 k&Omega;.