Yep - thanks for the replies. Shorter cranks will definitely be my next upgrade.
Well, I went to my LBS yesterday to ask about this. They just took off some new 165mm cranks from another bike (the customer fitted a power meter). They offered a great price, so I'm getting them. Will be interesting to see if I notice a difference (not just toe overlap, but in other aspects too).
Transition to shorter crank (as i did go from 172.5 to 167.5 to 165 before)
-Saddle height should go up 3-5mm as your crank is now 5mm shorter.
-relearn the gear! you theoretically need lower gear at higher cadence. 170 down to 165 is only 3% difference though, one gear in the back is usually 6-12 percent different per gear. 52 vs 50 in the front is 4% difference.
Reason is: reduced torque of shorter crank make it feel like a harder gear. Pedaling circle is now smaller too (smaller circumference) if you move the foot at the same linear speed through smaller circumference, that'll naturally result in higher cadence without anymore effort. And if the crank was too long from the beginning, going down will not reduce your torque much as your leg's improved efficiency will offset it. So, it only improve things.
-it takes quite a few weeks to fully get used to it. Good luck and keep an eye on even shorter cranks!