Query vs Datastore?

[thincom2000]

When working on some of my hacks, I have come across this dilemma:

Should I add a new table to the database, which will then add a query to every page OR

Should I add an entry to the datastore, which wouldn't add a query? I believe this would be fine with light use of the hack, but for others who use it more religiously, several hundred or thousand rows might be constantly loaded into memory on each page - and then sorted and processed (where a query would only load the 3 or 4 necessary rows).

I'm not aware of the ratio of server load between MySQL queries and memory usage. I realize every server would handle this differently based on their hardware, but since I am considering this for public release of hacks, which is the most advisable method?