new 50D or used MKIIN?

Hey guys,
I just sold my 40D and a bunch of Canon lenses, but I am keeping my 400 f/5.6L until I can afford a 500 VR:D, until then I want to use this lens with either a new 50D or a used 1DMKII N (max budget for body $2K). Which one has faster/better AF for BIF? From Canon technical documents and online reviews 50D has the same AF module as the 40D but I have heard some BIF experts here say the 50 has better AF, and of course people here are most credible. My experience with 40D AF was it was pretty quick but it could be very erratic especially when bird is against foliage in BG, my technique is AI-servo center AF point only, pump the AF-ON or shutter button periodically when tracking the bird forcing the AF to pick the bird but still I was getting many many full blown AF shots:( my D700 can nail the AF in similar circumstances.
Is this issue improved with 50D or should I get MKII N?
I have spotted a clean MKII N for $1700, need to decide quickly.

Thanks:)

The AF on the 50D is amazing compared to the 40D. I wouldn't have believed it unless I had first hand knowledge. The tracking is also amazing. The only thing I am not happy with on this 50D is the noise. I am happier with the performance of the 40D in relation to noise. I have not yet tried it with the noise reduction feature, but I was hoping for better results without even trying it.

Hi Arash... I own all three bodies, 40D, 50D, and a mk2n. The 50D wins hands down when it comes to AF. Really super in that regard. Everyone complains about noise, I find it to be very acceptable, you just can't underexpose or bad things happen. (I do not use the in-camera noise reduction) I do have trouble with a magenta color cast in cloudy conditions. I'll post an image in avian that I took today, I would likely have missed focus with the mk2n or the 40D, but the 50D grabbed fast and hung on. Good luck, hope this helps.

Fully agree with Grace The 50D can produce clean images if exposed properly. Images made at 400 ISO are just fine and images beyond can be cleaned up with Topaz which works much better than Noise Ninja, both in cleaning and keeping sharp.

Do like the images coming out of my Mk3 better but the extra reach from the 50D is nice.

Thanks guys, I know about the noise but I won't push the ISO any higher than 400, for everything else I have the two kings of high ISO. my only concern is AI servo tracking for BIF. So I will pocket the 600 bucks and order a 50D:D