You may be interested in one of my many irrelevant but inevitable testings (I did this one last year when looking for trouble with Ableton, literally):
Setup:
2 x Ableton Live running on Windows Vista, each using their own stereo output pair of a FF400, both playing the same audio files, but one phase inverted. Both pairs were digitally summed via Totalmix for output.
Now comes the interesting part: Both instances of Live were MTC slave synced to a single instance of Midi-Ox via MidiYoke running on the very same computer.
Result:
Complete cancellation, which to me looks like sample accurate synchronisation. Ableton support denies that this would be possible, but obviously it was back when I tested it.
That was before they "fixed" Live's Midi slave behavior though, from rough rounding to the next full integer BPMs to unrounded very bad calculation that's mostly off. Didn't have a look at MTC sync after the "fix", so maybe MTC was affected by rounding, too and thus the two instances could sync so perfectly against each other.
Whatever, both Midi-Ox and MidiYoke seem to be up to the task when it comes to Midi Sync, most likely LoopBe would be, too. Don't worry too much about CPU load. Even when most applications still cannot deal with Midi properly nowadays it's nothing that stressed the CPU any much.