I too have Win7-64, 8 gigs RAM, and SPLAT.  I've had projects 5 min long and 70 tracks running, and maybe I've witness some RAM being slowly gobbled.  Maybe not.  HOWEVER!!! I periodically save and rename (v01, v02, v03, etc.), and exit from Sonar, then reload.  I've always done that routine, not only with Sonar, but also with Word, Excel and other programs.  Why?  Because everything eventually takes a crap, and when it crashes, can take out weeks or even months worth of grueling work.  I've never had Sonar do this, but I have had Word take out an important document that almost caused me to get canned from my old day job.