John,
what I want to test is the 200mm F2.8L + 1.4TC against the 400mm F5.6L just to see whether it's worth the investment. From both everything I've read and everything I've seen, the 400 is a really nice "affordable" super-telephoto. Whether or not I can justify it based on revenue potential is a key question because I won't be able to "sell" it to Linda for my wildlife adventures.

That one will test my creativity .

Jim