I'm currently riding on an unsprung beater saddle. The pavement on my main errands loop is pretty beat to hell... I grew up in Pennsylvania and thought I knew what big potholes looked like. Madison potholes look like what I'd call a sinkhole *g*. For an unloaded ride (just my 165 lb self), the saddle is fine. I can use my legs as shock absorbers for bumps, and things are peachy. Current max distance is 10 miles, and is going up. Slowly.

For a loaded ride (my 165 lb self + 30-45 lbs of stuff in a backpack), I end up in pretty serious pain after just 2 miles on bad pavement. The saddle bounces if I pedal hard. It's harder to absorb shocks with my legs. End result is I hurt and sometimes get saddle sores. I could probably go longer on good pavement.

With the load in panniers on my rack, things are not as peachy as when I'm unloaded, but they're still pretty good. I haven't hit my limit with panniers yet. I'd expect it's less than my unloaded limit, but not a lot less.

Springs probably aren't something I need for utility riding with panniers, since that's mostly short trips. I may need 'em if I start doing centuries or touring. I have to hammer pretty hard to get the bouncy saddle effect when I'm not loaded down. But just one rider on one bike has different saddle needs at different times, so the trick is to figure out what *you* need. And well, there is some trial and error involved