Well at least it is a European Towing thread
Okay, to clarify (non-Volvophiles should obviously tune out now!):
The turbo anti-sway bars are not IPD ones; they are actual original Volvo ones I took off a mid-80s turbo wagon at a pick-n-pull. IIRC my original bars were 21mm front and 16mm rear, and these are 23mm front and 21 mm rear - but I need to check that in my notes. At any rate, these figures are proportional to the change. (I think the IPD bars are 25mm/23mm for NA cars, or 25mm/25mm for turbo cars, but again I need to check on that; at any rate my new bars are about halfway between stock and the IPD ones, and I'm quite happy with them.)
At first this was my only change, after years of driving similar 245's with bone stock set-ups. OMG... LOVE!!! The car suddenly handled like it was on rails, and I could do cloverleafs at posted speeds, swerve to avoid other cars, and just have fun on corners. There was no excessive tendency to oversteer (as you know, they are set up to understeer in factory trim).
Next, I went from the "as I bought it" rear shocks to a set of Boge Turbo Gas (stock on turbo 240s; on previous cars I'd used the OEM Boge Automatics). This made a slight difference, but really only to go from "augh, I must replace these horrible old shocks" to "Ahhh, new shocks." With this set-up the car handled great, although since the rear springs were a teensy tinsy bit saggy, the rear end sagged when towing.
Next, I added the overload springs. My mechanic, who is new to me and my car, drove it after installing them and said "OMG, what is wrong with those shocks?!" I, knowing just how the car had felt when I drove it in (and of course knowing the shocks were newish and fine), drove out to see how it felt. Augh.... awful. It wasn't so much that the car *bounced* (the shocks took care of that), but that the rear end suddenly felt "dodgy." Like it could bounce sideways into the adjacent lane (not that it WOULD, but just the way it felt). All my wonderful improvements that I felt when I put the larger anti-sway bars on were GONE. And on a long freeway trip, I found I had to recline the seat *way* back just to not feel Every Single Joint in the road surface. Yuck!
When I picked up my tall/heavy friend, and all of his and my gear were in the car, it was not bad, but that was quite a load (I normally carry quite a bit of stuff, toolboxes, and etc. but that didn't calm down the springs at all).
So I have a dilemma: Leave the springs on, which would probably be quite nice when towing (I carry a fair bit in the car then, plus have the tongue weight); or take them off and have a well-behaved car 95% of the time, and a car that has behaved fine towing as it was (albeit the rear end was not "perky" when towing).
If I take them off, I have either the original springs from my previous 245 (not saggy when the car is not loaded), the springs from this car (were a tiny bit saggy), or a new set of "normal" springs. I haven't decided how to proceed yet. I had not heard about the springs "breaking in," and I don't think IPD mentioned that.