I'm not sure if the overhead of MD5'ing a 5M file is worth it in hindsight.
There shouldn't be much noticeable overhead for generating an MD5 on a 5 MB file. I trade (legal) hi-fi concerts as.SHNs (no loss) pretty frequently, and the filesizes frequently run > 100 MB per song. Generating an MD5 for a file this big takes 10-12 seconds.... so unless you're adding music to your collection like a madman, there shouldn't be detrimental effects of MD5ing the entire track. HTH.
Yeah, umm... didja get that memo?
All your McTrademark are belong to us(TM).