To get things back to simple terms, as has already mentioned, today's high ISOs are far cleaner than yesterday's. I had a Nikon D700 - arguably the first (along with it's big brother, the D3) camera to really grab low light levels and render them cleanly. I have now got a D5300, a cropped sensor camera who's low light capabilities and high ISO cleanness are far superior to the D700. Everything moves on. Whether it is back-illumination or the latest materials, micro lenses or anything else, things will only get better. You will not be disappointed if you purchase an up-to-date crop-sensor camera.