I have SPC lowers with the ride height kit on the shelf, I bought them last summer. I like the ride height adjustability and the caster to hopefully stay centered in the wheelwell. I don't know how big of concern that is for some but it made sense when comparing apples and oranges.
I took that into consideration for about 3 seconds when I jumped on the bargain I felt I got them for.
I still haven't nabbed any upper control arms but the "needs" list is getting a little shorter on the big items... for now.
I was confused by your "650 lb 2+" lower coils (existing, possibly 680 lb)" comment.
2+"
With my still evolving kit I anticipate a front coil spring change. The ATS spindles I have incorporate a 7/8" drop. I have Hotchkis 2" drop coils now. Then the SPC lowers have 1" drop, but I read it is more like a -1.5" to +1.5" range so 3" of leeway to make corrections. I would prefer to have a spring that puts me in the middle of that and then work from there to tune, mostly for appearance.
As it is, I am looking at 3 7/8" advertised drop but we all know it varies from car to car.