500mm vs 600mm?

Don Lacy wrote:

jjl wrote:

I'm in the market for one of these lenses, and looking for feedback from people who have one or both, and perhaps wish they had the other one. I'm just looking for insights that I might not have thought of. I know all the specs, weight, etc... I will probably rent one first just to get a better sense of it.

At the moment, my longest lens is the 400 f4/DO (plus a 1.4x extender). It's been a great lens, but I crop most of my final photos with it. Seems I can never have enough length. I'm at a place in life where I can afford a 500 or 600, but not both (let's not get silly). I'm mostly shooting birds, and it's all for fun (though I do professional work in unrelated areas).

I'm leaning toward the 600 (new generation lens), because I feel I can never have enough length. The number of times it's "too much tele" will outweigh those where it's not enough. One of the reasons I picked the 400 f4 years ago was that it was light & I could use it hand-held if needed. But, in practice, I almost always use it on a monopod anyway. So, why not have a longer lens?

I've considered going with a used first-generation, but feel like I'll have regrets. I've also considered going with a refurbished 600mm to save ~$2000 or so, but at this price range, I'm not sure if that's a risk worth taking... or is it a risk at all? Maybe a refurbished 600 is totally fine, and it's just a vanity thing? Anyone out there have a refurbished 600?

Any insights, lessons learned, etc that anyone can share before I pull the trigger on this? thanks in advance!

On a crop body the 500 is more then enough lens for birds I rarely find myself focal length limited. If I was using a full frame body I know I would want a 600 it makes little sense to me to either crop for reach or buy a lens that a TC is going to live on.

What do you say to someone trying to increase reach while sticking to a budget and considering the 400 f/5.6 + EF 1.4x III combo?