Choose the resistence with voltage divider sensor
Ah, I once wrote an absolutely fantastic answer :-) for that!

I found that you get the maximum output range if the series resistor is equal to  

\$ R_S = \sqrt{R_{MIN} \times R_{MAX}} \$

You'll have to admit that this just looks beautiful. So for your sensor that would be 

\$ R_S = \sqrt{23 k\Omega \times 65 k\Omega} = 39 k\Omega\$

If you feed the resistive divider with the ADC's reference voltage you'll get readings of 
380 and 640 for 23 k&Omega; and 65 k&Omega;, resp. That's a range of 260 discrete values, or a 0.4 % resolution. You can't get better than that without amplification or a higher voltage difference across the resistive divider. 

Note that using the same supply for the divider and the ADC's reference the reading is completely independent of voltage variations!