Let's take a look then at AF speeds
K7:
http://www.imaging-resource.com/PRODS/K7/K7A6.HTM
"Full autofocus shutter lag using single-point (center) AF mode is excellent, at 0.093 second with our reference Sigma 70mm f/2.8 lens. Switching to auto-area AF mode increased lag slightly to 0.108"
No A580 results from them yet but they have the A560 ones:
http://www.imaging-resource.com/PRODS/AA560/AA560A6.HTM
"Looking at the Sony A560's ability to determine that it's properly focused when shooting the same target multiple times, its speed is a little slower than average for a consumer model when using the optical viewfinder. The A560 required about 0.295 second for full AF using the center focus point. This increased slightly to 0.307 second in wide-area AF mode"
Let's look at the A55:
http://www.imaging-resource.com/PRODS/AA55/AA55A6.HTM
"Looking at the Sony A55V's ability to determine that it's properly focused when shooting the same target multiple times, its speed is about average for a consumer SLR. The SLT-A55V required 0.22 second for full AF using the center focus point. This decreased slightly to 0.218 second in wide-area AF mode"
For fun the K-x:
http://www.imaging-resource.com/PRODS/KX/KXA6.HTM
"Full autofocus shutter lag using single-point (center) AF mode is excellent, at 0.097 second with our reference Sigma 70mm f/2.8 lens. Switching to auto-area AF mode increased lag slightly to 0.122 second, but that's still very fast for a consumer model"
D7000:
http://www.imaging-resource.com/PRODS/D7000/D7000A6.HTM
"the Nikon D7000 was slightly slower than average for a prosumer SLR. The D7000 required 0.238 second for full AF when using Single-point (center) AF mode (our default full AF lag test), a little slower than what we measured for the D90 (0.208s) and D300S (0.225s). The D7000 required 0.436 second when using the 39-point Auto-area AF mode, also slower than the D90 (0.270s) and D300S "
Nikon are not known for very fast AF Canon are considered faster in general. Of course AF speed does not always tell the whole story because tracking and accuracy are also very important. Having used and owned a number of models from various makers I'd say IR's AF figures are fairly near to actual use obviously different lenses etc will influence that.
I'm not seeing the slow AF you're talking about.