Lightroom :: What Is Practical Maximum Number Of Photos In LR4 Catalog

I realize that there is no preset limit in the number of images that can be saved in a single (Lightroom 4) catalog but I need to know that given a  well equpped PC  (system with 2 sockets/8 cores,  8+GB of memory and plenty of fast hard drive), how many images can be _reliably_, and with acceptable performance, kept in a single catalog ?
 
So far I have been maintaining 1 catalog per year for my images but creating collections or galories that span over several years has become a pain so I am considering consolidating all the catalogs into one, which would then contain well over 500k photos.
 
I am a software type and am aware that the LR implementation does not impose internal hard limits on the individual dimensions it deals with but I would like to know:

- What are the sizes of the catalogs that the software is being stress-tested with before it is released (rough numbers would do)
 
- Is it possible that an internal _incoonsistency_ could be introduced in a part of the catalog that would go undetected (by the global consistency checking) and would only surface when you try to access that area which may not have been touched for many years (in other words is it possible for the catalog to become _partially_ corrupted and yet pass the (checksom-like ?) verification that takes place when the catalog is being backed up ?)
 
- and, in case it matters, there are mostly raw images, ranging form 10 to 50 mega pixels each (not that these should impact the size of the catalog.)