I'm still thinking for pure bulk (no strength/performance goals), 3x per week is better, with slightly less volume, but the studies may disagree with me.
However, if you're doing 4 split programs a week (twice per body part), you're still stimulating your growth hormones 4 times per week. I don't know how much growth hormone stimulation is local and how much is systemic, but it makes sense that if you load your body more often with big compounds, but each bodypart gets loaded less often, then you'd be getting the best of both worlds.
But if we followed that logic we'd end up with 4 day splits again...
We know once per week isn't optimal because its too infrequent, we know 4 times per week (per bodypart) isn't optimal because there's not enough recovery time, but whether 2 or 3 times is better, well I think its much of a muchness, noone's achieved significantly better results with either.
From a physiological viewpoint, 3x per week would be better for growth as it creates a more frequent anabolic envirnonment, and 2x per week would be better for strength as it gives the CNS more time to recover and adapt, but when we're talking about load does your body know if its straining for bigger muscles or more strength? I don't think so...
So enough rambling, bottom line is I've never heard of anyone achieving significantly better size or strength improvement from switching between 2 and 3 times per week. They both work about the same.
