I'm using OEM ITR springs on my Koni Yellows. Got 50cm of snow over the last few days, no problemo. The front will drop about 1.5" - .75"
I haven't actually started the swap but I have a general idea of what to do. These websites helped me understand what I will be looking at to do.
The only after market spring I know of that has higher spring rates than stock with oem(ish)ride height is H&R oe sport springs. IIRC those springs