Don't entirely agree with you there Jay, wouldn't say that it was as dangerous as you are implying. I did ask on here a while back if anyone knew the standard factory spring rates but had no replies. Quite simple - if they're too soft, the car will bottom out/coil bind severely to the extent of a serious lack of ground clearance (could bash the sump), cornering would also be interesting as the suspension would have no or very little travel, as I experienced with too soft a spring & not enough travel, the bottoming out is bloody harsh & extremely uncomfortable. In this case, if they were to be too hard (doubtful) you'll get loads of ground clearance & the ride would be stiffer but possibly not mega harsh as you'd have no coil binding - as I said, I doubt very much if a petrol engined car has stiffer spring than a diesel.
Put them on a scales, squash them an inch & take a reading - not hugely accurate but it will give you some idea! I used our pallet weigher & the fork lift with a pallet of good on it to sqeeze the spring!!!!
Surely springs aren't that expensive - just buy new ones!!!