Canon 70-200 f/2.8L IS II vs. Canon 100-400mm f/4.5-5.6

I currently own a Canon 70-200 f/4.0L IS lens, a Canon 300mm f/4L IS lens and a Canon 500mm f/4.0L IS lens. I primarily photograph wildlife and I do a lot of walking around. The 300 was my first lens 'cause I couldn't afford something larger and I thought it would be a good all purpose tool. I haven't been disappointed. However, sometimes when I carry the 300, I wish I had the flexibility of the 70-200 with the 1.4x tc. And, sometimes when I carry the 70-200, I wish I had the added punch of the 300 + 1.4x. Sound familiar? Note: I'm keeping the 500!

Now, if Canon came out with a new and improved 100-400 zoom, I might trade in the 300. But the 300 is a superior lens and I'm thinking about another option.

First, price is not an object for this discussion. I'm considering trading in my beloved 70-200 and 300 prime lenses for the Canon 70-200 f/2.8L IS II as a general purpose lens to be used as is, or with either of the two teleconverters. Ergo - a 140 to 400mm lens with better (?) performance than a 100-400. All of the reviews I've read give this lens the highest possible marks with or without the tc's.

Now, the 2.8 is about twice the weight of the f/4.0 70-200 but about the same as the 100-400 lens without a teleconverter. And, there must be some good carrying systems that make carrying heavy gear more comfortable than using a shoulder strap.

So, I'd appreciate your thoughts - both technical and practical.

Thanks

I'd be quite surprised if the 70-200 + 2X teleconverter had equivalent image quality to the 100-400mm zoom or the 300mm f/4 + 1.4x. The 70-200 f/2.8 is a good lens but the 2x teleconverter is rather notoriously poor (noticeably worse than the 1.4x converter, in particular.)

Perhaps the new 2X converter announced yesterday will change this calculus. Time will tell. However unless you really need the 70mm end, I suspect you'd be happier with the 100-400mm zoom. It may not be better than your 300mm f/4 + 1.4x, but it should outperform the 70-200+2X on the long end.

I had used the 70-200 f2.8 L IS USM + EF 2xII combo, but was not happy with the results at f5.6

The new 70-200 f2.8 L IS II USM plus EF 2xIII might be better bet. Lets see when I can get time and the lens to test. You can try a holster case on your belt to carry a camera plus lens. Hanging it around the neck is not ideal for long treks.

Cheers,
Sabyasachi

Thanks for the comments. I had understood the first version of the 70-200 f/2.8 L IS USM + 2x to provide excellent results, thus my consideration of the combination. I'll be awaiting Sabyasachi's analysis plus the opinions of others having first hand experience.