It's not that mountains that stresses the joints, its the very steep inclines out of driveways, going into and out of gas stations, basically they "funnel" rain water to places and they use steep curbs and driveways to do this. If you were to take these straight on in some cars they bottom the front or rear of the car on the ground because they are so steep and inclined so sharp from the terrain. In MN we don't ever have any of this, as snow plows would have a really tough time. It's silky smooth there from that aspect.
As you angle into and out of these steep inclines I imagine its not friendly on the bushings. lots of cars do a 3 wheel balancing act when going over them with stiffer suspensions.
so typically on any car I have ever owned, you place your hand at the 3pm and 9pm position on the tire and try to move the wheel back and fourth at that position. the wheel should have zero play in the system (should also have zero play at the 12 and 6 position as well but that is checking other things). I was able to move the wheel a good amount even with new bushings, which makes me think the rubber bushings aren't adequate (atleast for the control arms I purchased). This is where your toe in and out moves when you drive the car and also all the slop in the left to right transitions. I drive my car VERY conservatively and average 36-40MPG, still have the original brakes on the car at 125K miles and still have a lot of meat on them. I am on my third set of tires. The car is NOT being driven hard at all.
Now I am not exactly a weak person, 6'2" 230lbs and lift a lot, so when I apply pressure its with a frame that size and I often times overlook how much stronger I am than others. I didn't exactly strain myself to flex the rear vertical bushing a good 1/8"+.
I also set up a well modified mazda rx7, went to poly bushings from the old rubber ones and tightened up that car a lot, handles like a dream. Poly bushings will transmit more noise and feel harshier on the road, I don't promote them on a stock car, but when the bushings new have this much play, I didn't want to mess with it anymore, so I went poly and will deal with it.