Any answer you get in this forum is going to be a guess. The real answer is to do a little benchmark testing. There is no set answer because it varies by processor speed, RAM size, etc.
A bigger factor to consider is how many people are searching simultaneously. The more queries you have, the smaller it needs to be if you want decent performance.
Lastly, the site doesn't say whether or not the software builds an index. (I suspect it doesn't). Indexing can be done in a database or with external indexing software and it will make your search about a gazillion times faster.
