how can i modify my 240's suspension without hopping too far down the rabbit hole?

hi everybody. i'm trying to make some decisions on my suspension setup without taking it too far. ultimately, i want a sporty ride for having fun on the streets.

what i've done so far:
14x6" alloys with 215/75R14 cooper cobras
lesjofors stock springs
volvo dampers all around
ball joints and tie rods
meyle strut mounts and bushings
23mm front and 19mm rear anti-roll bars

i also have bne select strut mounts waiting to be installed after i decide which direction im going with my suspension. the handling so far is better than any car i've owned before. although i believe that is mostly due to its lightness and lightness distribution. however, my rear end feels under-damped and is very noticeable when going over speed bumps even at very low speeds. the solution is simple: just get stiffer dampers. this is what i'm going to do regardless.

but i can't help being tempted by the idea of lowering the car a bit with a set of sport springs from ipd or b&g. i would love to make the handling more sporty and sit a little lower to the ground. i'm afraid that by doing so, i'll be causing some problems like putting the front roll center too low and screwing up the alignment of the rear axle.

basically, are sport springs worth the hassle? will the car handle noticeably better? am i going to screw up the geometry of my car?

just out of curiosity, i measured my lesjofors stock wagon replacement springs

13.8mm coil diameter front
14.2mm coil diameter rear

based on what i read on anthony hyde's page (https://people.physics.anu.edu.au/~amh110/Handling/volvo_sports_handling_V2.htm) and assuming the thickness of the paint on the springs, the actual numbers are probably 13.5mm for the fronts and 13.7mm for the rears.

assuming my rear springs actually have a 13.7mm coil diameter, they should have a spring rate of 290 lbs/in. given the motion ratio of 1.5, that equates to a 435 lbs/in spring!

no wonder my rear end feels under-damped with stock volvo rear dampers )

I wouldn't really consider the ipd springs stiff by any measure. It'll lower the car some but will ride similar in stiffness to the OE springs.

speaking of, your OE springs are no where near 435*. They're closer to like 75*. I can't remember where on here I read it but OE turbo springs were like 125* up front and 100* rear

you're probably right about it being nowhere near 435 lbs/in. maybe anthony is referring to both springs in combination? maybe he already accounted for the motion ratio as well. the next lower rated spring according to his website is 13mm. much lower than the 14.2mm i measured.

My grey car had 300* front and 200* rear springs with Koni yellows and that car was stiff AF compared to the stock volvo springs.

so my lesjofors gt-like springs are already 15mm lower than stock and youre saying the ipd sport springs are probably no stiffer. so the only difference would be the fact that the ipd springs are maybe 1 inch lower than the gt springs. i wonder how much of an effect lowering the center of gravity an inch would have on the handling.