Tanveer, if you judge every dSLR by their ISO performance, then you can never consider anything outside of Canon. In the film days I never really used anything above 200ASA. Once I bought 400ASA and 1600ASA each just to check it out, but that's about it. Also, in the film days we never cropped, that's a term I heard only after switching to digital.
I am quite happy with the high ISO performance in the Thai boxing images few posts back. The chances of shooting high ISO and needing cropping would be a rare requirement for me. Therefore I am not really worried about it. I am not going to eliminate an excellent dSLR based on such an obscure need.
Being a life long gadget freak (I have improved a lot in the recent years) I have often bought gadgets based on some obscure need, and then never use that feature. These days I buy equipment based on their ability to meet my major requirements. The reason I consider E3 are follows:
1) High speed AF specially in low light, that's a big problem in E-500 now.
2) Handheld indoor/lowlight photography. With E3 I can use both IS and highISO to maximise my chances of good photos. And I don't really care about cropping here.
3) Articulating LCD screen for composing. I hugely miss this feature since it is so handy in my Sony F-717. It is one of the reasons why I still hold on to my F-717.
If not for the above 3, I would happily settle for E-510 which is a bargain now.
Its not an obscure need. I have used high ISO to compensate for the cheapo slow tele lens.
I guess will in body IS which can give me guaranteed 2 stop improvement in 600mm(300mmx2), high ISO is not needed.
But if you want to shoot action, you may need to bump up ISO, and except for Oly,Canon/Nikon/Pentax all three offer clean ISO 1600
Hehe, Looking at the people here, I think I am a very obscure photographer
Many shots I have taken were at at 50mm F1.8 at ISO 1600
In couple of cases I underexposed and then in RAW pushed up the exposure making it effective ISO 3200.
But then with a IS in body, you don't need all this circus.
Coming back to E-3 I saw a few samples with the sigma 50-500(whopping 1000mm). They were quite good. Handheld moon shots.