I have added H&R springs to my car and the ride is a bit rougher than I like. However the handling and look is great. I already have winter tires on 15" rims, the ride is much better on the winter tires.

I had planed on getting high performance summer tires but as far as I know they all have a very stiff sidewall for better handling but worse ride. If I put the stock springs back in I could probaby use summer only tires and have an acceptable ride.

Or I could get a tire with a softer sidewall and leave my H&Rs on. The Conti Extream contact, Dunlop A2 or RE950 are all rated highly for ride comfort on tire rack. I was hoping one of these tires would soften my ride a bit but still give good performance. They would also last longer and let me get through a late spring snow without sliding off the road.

Which combo would give the best handling? Will softer sidewall tires make a noticable difference in the ride?

 

Lower will almost always yield better performance. Lower center of gravity. I had mine lowered w/ intrax springs and regular all season tires and it handled fine.

 

The ride should be a little bit softer if you get Tokico Illuminas, or almost stock if you get KYB GR2s I however have not been in a car with them so, if anyone have them feel free to chime in. AGXs are really stiff, and the adjustment only changes the rebound, so lowering the setting won't do too much.

 

i have the Tokico blue struts. and ST lowering springs. the ride is not harsh. it is stiffer, yes, of course, but not really so much. i also have ST anti-sway bars front and rear, and a Stillen FSTB. i use the Michelin Pilot HX tire. very awesome handling. the tire choice highly "enabled" the suspension. the ride did become harsher when i added those tires as they are only 50s. the factory spec tires are 65s. so your theory is true-ish: a softer, well, taller or fatter, tire will offset a bit of the harshness of the high-performance suspension mods. to make an extreme illustration - the difference between a rubber band around a steel rim versus a marshmallow around it - you will lose some handling and response with phatter tires. but you will gain some small measure of 'comfort' if that is what you really want. there is no free lunch.