Unneeded and Name check needs to calculate a hash to determine if the name is correct or not or if the file is totally unneeded.
The checksum checkbox stands for testing checksums in general (rom/chd, sha1/md5/crc32 depending on further settings) is correct or not...to show or not to show a warning about a bad checksum. If you toggle checkboxes after a scan you can toggle (hide/show) the belonging results.
So if you need to go for speed (a ssd or a good hd cache and recent cpu by the way should be ok, too), you can turn off the unneeded/name check...and only keep missing enabled....
So...I've just checked a progetto snaps archive (34.800 pngs)...on a common hd (not ssd) and a full scan with everything (name, unneeded, checksum, case, etc..etc..) enabled took 2 min 47 seconds without diskcache....another one with diskcache only 38 seconds....
and with only missing enabled (and not checksum, etc) only 7 seconds...I guess that what users can live with.