What specific case do you have in mind ?
As already said by frenchie, it depends of the mATX case. Do you want a really small one?
However, in an enclosure such as the venerable Antec NSK3480 (or as the Silverstone TJ08/TJ08-E) almost anything should fit (anything less tall than a Thermalright Archon, or less wide than a Scythe Susanoo, I mean). One of the most recent 3480 in the SPCR gallery
However, if I may take the liberty, I mean that you may not need such a solution for a database server.
IMHO even a smaller heatsink, like the Scythe Big Shuriken, might suffice more than enough, without any noticeable trade off with reference to quietness or cpu temps (I have a MS SQL system - but mostly for development - running on a 3.0GHz quad core AMD with that heatsink).
Then, even the enclosure might be smaller (as the quoted NSK3480 is a compact case, but it's not one of the smallest).