Not worth it to me either. The 100-400mm takes great, sharp pics, is $6000 cheaper, and quite a bit smaller and lighter too. I don't see a value in spending $6000 for marginal improvement.Mike Lane tested the Olympus 150-400mm ($7500 +/-) against the 100-400mm ($1500+/-) and found the 150-400mm images slightly better -- whether that difference, the internal TC and larger maximum f-stop is worth $6,000 is for everyone to decide for themselves, it's not to me.