The tests lately tell not even close to the whole story behind the sensor..even here it states around 2600lines resolution at 100iso...and holds to 2100 at 16,00 iso.

here is probably a more reliable resolution test 2900 lines of resolution...

even at 1600iso the a57 looks a bit less than 2100lines compared to 2100 at 16,00 iso for the a58 according to their test...
and the a55 will have a cleaner sharper image with more resolution than the a57 up to around 400iso then the jpeg engine starts 'killing resolution for noise control...
The a58sensor has more resolution, the colors look more natural, less sharpening artifacts on the a58. Obviously the noise control with the bionz sensor between the a55-a57 did wonders at high iso ...The a58 has an improved processor and more mps...more resolution all around.(and noise control)
Unless you want to shoot 16,000 iso all day long at 15 frames a second(and detail will be smeared or non-existant)..the a58 is going to put out better iq . If you shoot over 3200iso for regular shooting and the jpegs look just a bit too noisy, well then have fun and i am sure a noise free blob of tree leaves at 3200 iso is within reach at this very moment(no noise woo-hoo)
Sorry for being a wiseguy..the camera is going to be more/as capable than every alpha out there except the a99 in all around performance and iq ...and if you need the reach even more capable than the a99 in many situations.
If you need a nicer back screen or more frames a second then no its not......true story,brian