the 2.5mm doesn't sound much but when the pedal is at the bottom, its 2.5mm lower and at the top its 2.5mm higher for a total difference of 5mm. Some people will notice some will not.
For 165mm versus 172.5mm, that's a big difference most people will notice. If you notice that your seat position height and fore/aft moves by even a few mm makes a difference, then you will probably notice the difference between 172.5mm or 170mm spin on a bicycle with both crank arm length and go with the one you feel comfortable. If your inseam is short, you may prefer 165mm. Torque you have to generate is higher on 165mm but it would be easier if your knee isn't bent all the way. My performance was much better with 165mm instead of standard 172.5mm.