I would agree with you that it would be the height of folly to put a bigger sail on your present rig UNLESS you ALWAYS sailed in very light wind conditions. Since that probably never happens, the standard 170 mainsail would do fine.
I would like to lower my rig similarly to your setup, but I don't have the equipment (tools) or more importantly, the know how. IMHO, the 170 can be a real handful in gusty winds while single handed. My rule is if I see the slightly hint of white foam at the top of the waves, I don't go out by myself. If I'm already in the boat, I reef the mainsail to keep the heeling motion down as much as I can.
In effect, you've already biased your sail plan slight toward a reef. I've been considering having a second reef point put in my main. With that and my furling jib, I would feel more secure in going out on more gusty days. I suspect the original owner of my boat "turtled" it at least once. He only kept the boat for a few months before returning it to the dealer for a consignment sale. Earlier in the year, I replace my mast cap because the rollers were jammed. The old cap was full of sand, indicating to me a turtle into a sandy bottom. And I saw another 170 (the only 170 I've seen in the Seattle area) do a turtle on a gusty day.
So, I don't want to try this maneuver unless I could practice it on a nice day and see if I could "right" the boat by myself. On my sea trial, the dealer and I went out on a day that we probably should have passed on. All we had flying was the jib and a couple of times, I thought we were "going over". IMHO, the 170 could use another 100 lbs or so in the swing keel.