I have a 5D and 1Ds Mark II. I find the 5D is better in low light and I like the larger screen. I greatly prefer the build quality, control layout, and AF on the 1Ds Mark II.
In the case of the 5D Mark II, you'll pay a bit of a premium for the latest, while it sounds like you can get a bargain on the IDs Mark II. Either way, you're likely to have a great camera.
The 1Ds2 can do action too, and for many of the events I shot this summer the AF & resolution allowed for some nice captures. I got mine near the end of the season, but it shines when the planes are well off from my shooting position, allowing a decent crop. (I was using a 1D2n until I got the 1Ds2, and now the 2n is getting a rest)
The 5D does OK with AF on the center point. When I first got my 1DMK2 I ran out and did a series of tests, since I finally had a camera with "pro" AF. The results of cars coming straight at me from 30-60 mph where 70% keepers on the 1dMK2, 60% keepers on the 5D. So the 1DMK2 was better, but did not blow away the 5D.
These tests were conducted in the evening, so the light was not the best, and the vehicles were driven my daughter and wife so I could specify the approach speeds. All shots were take with a tripod mounted 100-400 L .
One major difference between the 1 series bodies and the others is the set of AF sensors known as the "ring of fire". They surround the center area, and if whatever you are tracking is somewhere in that set of sensors it's most likely going to be in focus when you shoot. The rest is up to you re shake etc, but that zone works amazingly well on small & fast moving targets. Following a small fast moving target with the center point is very difficult compared to using that ring set. All other things aside, that ring makes a 1 series body that much easier to use in an action situation where the target isn't the size of a person or bigger.
