I knew I had read about this specific idea somewhere, and I've finally found it... I know it's on another forum, but the guy who wrote it up did an incredible job (IMO). Here's a link to the complete write up:
Clicky
And here is an excerpt from his write up (in case you don't want to read the whole thing...
3) Can I put lowering springs on my stock shocks?
People tend to ask this question a lot, and the answer is always the same:
Of course you can, but I will never recommend it.
None on these forums, nor any reputable technician, nor any sensible car enthusiast will ever recommend the use stiffer springs with stock shocks.
When you’ve been around these communities as long as I have, you tend to hear all of the stories. There are always going to be people who put enormous drops on 1993 stock shocks and get away with it for 100,000 miles. It is possible, and it does happen. Then there are the people with 2004s who put on the springs that supposedly “work with stock shocks,” and their shocks are blown within a few days. These kinds of accounts tend to debunk the idea that the most important factor contributing to whether or not a stock shock will last is its age. Sorry, the age theory just isn’t true. If you are going to consider the shocks’ age, you also have to take into consideration the road conditions they were exposed to, how they’ve been driven on, what they have carried, etc. Still, none of those factors can outweigh sheer physics.
It remains that the single most important factor that determines whether or not your shock will survive is the spring that you place on it.
The bottom line is that stock shocks were not necessarily designed to handle springs that are much stiffer than stock. I know people want to assume that whatever happened to their buddy is what’s going to happen to them, but that’s not how it works with suspension. This is a very dynamic game, and you need to be prepared to deal with the worst case scenario.
Hope this helps!