Hi Malte,
Well, it is up to the server performance, but it could actually work. Once the keywords are in the database, it should be just fine. The problem can be the indexing process – it could take up a lot of CPU and RAM, regardless of how many pages are indexed, as the parser needs to open and decode the whole file either way.
I think you should give it a try. There is an indexing throttle built-in to the plugin, so it waits between two operations for the server to “cool down”, and all files are indexed one by one as well.
If you start seeing a lot of “error 500” or “bad request” errors on the site front page, or the server does not respond for a few minutes, then it probably can’t handle the files. In that case you can just simply delete the index.