Going to 175 made a difference for me, but I'm 6'2 and have a 34-inch inseam. You shouldn't have to adjust your cleats, but I'd lower your saddle 2.5 mm. And if you haven't done it already, get a professional bike fitting.
I've also experimented with 177.5, but not for a long enough period of time. Hinault's, Eddie B.'s , etc. older books seemed to suggest trying the longer lengths and giving yourself enough time to get acclimated to determine if they really are beneficial for you, but lately the focus seems to be on higher cadence.

It's noticeably easier to spin a 172.5 at high rpm than it is to spin a 177.5, but that could simply be because I haven't taken the time to become accustomed to the latter.