started with 170's, went to 172.5, now I have 175's.
I have no pedal strike issue and love the way I can crank up hills. My geared bike had 170's and I changed then to 175's.
Try a longer crank and see what you think.

I know it's hard to do a real scientific comparison. You would need 2 bikes set up exactly the same but with different crank lengths.

look at this and scroll down to crank length.....
http://www.peterwhitecycles.com/fitting.htm