Saponaria ocymoides is seeding around and almost getting to "weed" status in my yard, in spite of zone 3 cold and dry conditions, and clay soil (it doesn't need to be grown in sharp drainage at all here). I started pulling them out this year but will probably have to get serious about it next year.
I live in Calgary, Alberta, Canada. As I mentioned, it's zone 3 and a normal winter here has only patchy snow cover, though the last 3 before this one had unusually consistent snow cover... seems to be back to "normal" this winter. The low precipitation level here (~40 cm annual precipitation, with much of the snow melt running off while the ground is still frozen) allows many "alpines" to be grown in regular soil. That said, by all means, anyone interested in Saponaria ocymoides should try it themselves - it's the only way to know for sure how it will act.