I did the math in another thread long ago, and it came out to be a 3% difference in cadence gained/leverage lost when using 165's over 170's.
48/16 vs 48/18 is something like a 12% gear inch increase, so that's quite a bit more drastic.

Your point comes across, although in this case, it's definitely splitting hairs. I doubt OP could notice the difference between 165's and 170's. I bet very few could actually.