As many of you know, a while back I picked up a 1Ds2 (just before the 6D was announced), and loved it. The controls are a bit cumbersome, but it made nice pictures, with much less noise than the 7D until ISO 1600, but at ISO 3200 it just falls apart. A 5D2 will be similar, I expect. Good until you hit the ISO wall, and likely won't have Canon repair support much longer.

I got a 7D2 at launch, and the 1Ds2 ended up being neglected in favor of the higher-ISO capable and much lighter 7D2. Sports shots require fast shutter speed, so I often have higher ISOs. Late in the day, I just couldn't use the 1Ds2 anymore, so it just stayed home. But recently, going through my Flickr photostream, I noticed the 1Ds2 shots. They really stood out, and I got me thinking about upgrading to a newer full-frame. Which limitations would I be willing to accept to afford a newer full-frame camera.

Alright, so full-frame is nice, but are the IQ improvements I saw purely because of the full-frame sensor, or is it partially 1D specific? I know the 1D series does more work in analog before converting to digital, and it handles highlights really nicely. Would I be happy with the 5D3 or 5Ds, or do I crave some secret 1D magic, pushing me to a 1DX or something? I'm assuming the 6D won't keep up with my sports AF requirements.

So yeah, it's definitely worth considering, but if you cheap out too much, you might end up with a camera you can't always use. Try to avoid that. The 6D is newer, and has higher ISO capabilities, and can likely be found for a similar price. On the other hand, it's likely like the Rebel of the full-frame line, and has less controls. Is there a limitation of the 6D or a feature of the 5D2 pushing you to the 5D2 over the 6D?

If I get to the point where I am seriously considering the full-frame upgrade, I'd probably rent each body on successive weekends, and compare the results vs. price differences to try and answer the "Do the magic 1D secret sauce exist?" question. That may not make as much sense in your price-range, where the rentals costs would be a fair chunk of the body price, but that's my thought process about the upgrade...