I have both a sprung and unsprung Brooks. If my cadence gets over 100-102 on the sprung saddle, I start to notice a bit of bounce. If I go over about 110 on the unsprung saddle I may start to bounce. When my cadence is a more normal 95 or so I don’t notice a difference between the two saddles.
In terms of comfort I didn’t think there any difference. Then I went for a tour. After about 5 days in the sprung saddle, I realized my butt wasn’t sore. IMO, the difference was subtle unless I was spending many hours on the bike. Since then I spent more attention to the differences between the two saddles and concluded that the sprung saddle was indeed more comfortable for longer rides.
Hope my experience helps.