Is any fluctuation due to the DAW or is it due to the hardware in general? Is PT or Live so different that one would see a tempo difference?  If its due to clock variations can a DAW be at fault?  Will Big Ben help? 

Will Big Ben Help.. I believe the answer will be yes

Should be pretty accurate: the midi tempo is a 'meta event' with resolution of microseconds per quarter note.   Wouldn't seem hard to make that the same everywhere.  But in terms of practical experience, I've never compared one daw to another, or even one system to another, say with sonar running in different environments, different clock sources. 

Anyone here remember when Cakewalk was set to ~192 (or less) ticks per midi 1/4 note and then they kicked it up to 960? Now this isn't even an issue, but a long time ago computers weren't fast enough for a lot of tracks at the higher resolution. I would make sure both DAWs support the same resolution for compatibility of midi note data/tempo.