[outofrangefinder]

Thank you all for the interesting discussion. My problem is now solved, in a way I didn't expect myself. My local camera shop carried an A580 for the first time and I had a chance to try it out. Seems that Sony has tweaked the AF algorithm. With the A580, the AF doesn't hunt nearly as much as with the A700, the 70-400 now feels almost like a new lens. It's not as fast as the Canon solution, but fast enough for my purposes and I got what I wanted without changing system at a reasonable price. Unfortunately, the A580 has other shortcomings like the missing second control wheel, no program shift (oh man), the small viewfinder and the fact that you can't turn off NR in JPEG mode (it has only two settings: "Auto" and "weak" - so it loses details from ISO 400 upwards in comparison to the A700). In RAW mode, the picture quality is flawless and the live view option does come in handy sometimes. Plus, it might be one of the last Alphas with an optical viewfinder. I wish they had dropped the A580s electronics in a A700 class body and added micro AF calibration. Anyway, the A580 seems to be underrated a bit, because everyone paid much more attention to the SLT bodies.