I've seen tidbits here and there but even with a google search I can't seem to get a more definitive answer.

What are the details for overcharging a stat? I've seen that you can hit a soft cap and get "diminishing results".....Can anyone go into more detail?

Overcharging is just their creative way of saying "diminishing returns" for stats. Essentially once you hit a certain point you start gaining less and less benefit from it.

I experienced this myself but only with HP recovery, Stamina recovery and Magicka recovery.

I had it with maximum magic with extra magic pool food in addition to enchants.

Not sure how it work in details but guess it might work something like, over max you get something like square root(total magic-magic limit)+magic limit.

How more you push the limit the less you get back but its no upper limit. limit will increase with level.

You will reach the limit with good enchanted gear.