I made a decision - I bought used Canon 1D (classic). After some days it is time to write down some observations and compare this old monster to 5D mark II.
This "battle" will be in two parts - the first one with more writing and second part with more samples.
We all know what to expect from Canon 1D. It is robust, build like a weapon. When you take 1D into your hands, you feel reliability. It should work for years in difficult (weather) conditions. The rain at race won't be excuse any more to not take a photos.
Let's look at some observations.
User interface is old and very clumsy for users from nowadays DSLRs. When using menus, you must use two fingers and changing settings really isn't easy. This is also valid for reviews, where you get a usually photo on LCD by default. For looking at histogram I must change view every time. And looking at histogram is the only way to be sure your exposure is what you want.
User interface on 5D mark II is excellent and that is all to say about that.
LCD on 1D is small, with low resolution, with very washed colors. And what is also important - at reviews you don't have magnification. Should we talk about LCD on 5D mark II? I think no. You know everything. It is brilliant.
AF is another object to talk when someone mentions 1D. AF is really very precise. I can't say it is much faster then AF on 5D mark II, but it is very fast and accurate. It must be, because 1D can takes 8 frames per second and its primary destination is sport stadium. Whey you hold shutter, there will be a machine gun sound. Shutter lag and blackout are small and the voice of shutter is fantastic.
Unlike many writes about - I must say that focus on 5D mark II is very precise and fast. Maybe someone has different feeling because it isn't so fast when you finally press the shutter button. But this isn't AF. AF alone is very good, if you use central focus point. On others focus points you will find some unreliability from time to time, but I have very good feeling with AF on 5D mark II. Changing focus points is easy on 5D mark II, and not so simple on 1D (old user interface).
AI Servo and sports photography with 1D are really pleasure. On rally (autocross) I can't find an out of focus shot! Can you imagine? Fantastic.
White Balance is (like on other Canon DSLR) not something for Canon to be proud on. Auto White Balance is little better on 5D mark II, but it fails on shadows when sun is high. I simply can't understand how camera can fail so much. Colors are very cold in that case. Hey Canon, listen, read, CHANGE!
I use AWB and shot an Whibal card from time to time, so I can later find an accurate color temperature.
On some similar shots with both bodies I found that histogram on 1D was better distributed. Canon 5D mark II has a little underexposure, but this was just one simple test and we can't say this is a fact. Maybe difference comes from wider angle captured on 5D mark II. I will make some tests in next days (weeks?).
Canon 5D mark II has new battery LP-E6 (very hard to find this part!) - and it needs good battery. The consumption is big. Information about battery status is very good and you know where you are with your shots. On the other hand 1D uses old battery. Times and development goes on...
When we talk about ISO, then you should know 5D mark II is a king.
Here is 100% crop from photo taken with ISO1000 (a little underexposured):
crop photos taken with 1D. At least not a lot. Better be careful when taking a shot - if situation allows. It simply don't have enough pixels (4.15 MP). Well - if you use 5D mark II - you can crop. And you can crop a lot. It is 21 MP monster. Or you can print very large prints.
All in all - if you don't need big prints, 1D will be enough for normal life. The quality of files are very good (1D uses CCD sensor and has big pixels) so this is no excuse.
On Canon 5D mark II user can capture HD video. Old 1D don't has this feature, but - you won't believe - you can save audio (for notes with photos).
I tried Canon 580EX flash on both cameras. Results are very similar (very good), but on a long term we can expect that results from 5D mark II will be a little better (because it uses newer E-TTL II). If someone has problems with understanding of Canon's flash system ... click here for simple description.
1D has 1/500s sync time - an awesome feature for using fill flash. 5D mark II has much slower sync time.
An interesting information - file from 5D mark II is 39 MB and file from 1D is 3,8 MB long. A big difference especially when storage is in consideration.
And next - Capture One converts RAW (to JPG) from 5D mark II on my computer in 38s and RAW file from 1D in 4s. Can you believe? Can you imagine how much difference is this when you are back from wedding?