Have tried this and it seems to be exactly what I was looking for.
Have set the Cache to 500MB and have done some extensive testing. Single collection download, 3 collections download at the same time, downloading a collection at the edge of the retention of a provider with a lot of missing articles, while setting up the fill server to 1 connection so that it can not catch up.
It all worked ideally!!!
When closing Alt.Binz the cache is saved to disk, all works just fine and the decryption speed when using the memory cache is fantastic! The only downside I noticed is that when Alt.Binz crashed (I am getting a lot of those lately, mainly when I press the connect button twice in order to activate new passwords for the servers), all the cached articles were lost. You would say what would one expect? If Alt.Binz crashes, of course the cache will be lost. The thing is that these articles that were in the cache were considered as permanently missing and there was no try to download them again. So par2 files were downloaded to repair the rarset. In most cases, if the cache size is relatively small, this should be no problem. If things are tight (lots of incomplete files, or no par2 files available), then one can still manually import the NZB again.
In any case Article Caching is a great feature! For anyone that has missed it, like I did, I would strongly recommend that they activate this as soon as possible!
Thank you RDL for another great feature!