As in the title ive noticed that i havent been very happy with my rebel t3i and its tendency to create noise (even at low ISO) and decided to start saving up for a better body camera and sell my camera with 3 filters for about $450. the only lens i have right now is a 50mm f1.8. Ill probs just buy a camera body and stick with the 50mm for a while. I primarily shoot automotive photography. Im torn (and confused) on the differences between a 6D, 60D, 7D, and 70D. what are the extra "0's" mean? I dont wanna spend more than $1000 on a body and will probs buy one off craigslist or used off amazon. Would it be risky to buy refurbished off amazon? Can anyone point out the main differences between these 4 cameras and tell me what will be the best buy for me? any help is hugely appreciated! Thank you!
Well if your wanting to stay under $1000 for the body you can scratch the 6d, 7d, and 70d off your list already. The 70d I think is running at roughly $1100 so that might still be within your acceptable budget range. The 6D is a full frame camera, the 7d, 60d and 70d are crop sensor cameras. The full frame will give you the better lowlight performance you want, but it's way out of your listed price range. The 70d will give you a little bit better low light performance than your current T3I, but not really by very much. It has a slighly higher boost ISO but the noise factor will remain about the same from what I understand. It's also a couple hundred dollars above your budget of $1000.
The 60d uses the same sensor as your T3i and the lowlight performance is going to be pretty much exactly the same as well. If it were me and I were looking for better lowlight performance with your listed budget, my recommendation would be to sell both your T3I and your 50 mm lens and switch over to Nikon.
You could purchase both a D7000 and a 50 mm prime for it for under $1000 and it will give you better lowlight performance than your current T3i, or go with the D7100 which would give you even a little bit better lowlight performance than the D7000 - though the D7100 would be a little more expensive, you can still get the body for under $1000 though you would go a little over that when purchasing the lens as well - but of course since you'd be selling your T3i as well as your current Canon 50 mm you'll have a bit more money in your budget so the D7100 would probably still be quite doable.
Both the D7000 and the D7100 will also give you much better image quality than the 60d and even the 70d, in fact the D7000 would give you about the same quality of image you could expect from a 6d and the D7100's image quality is even better.
Now the 6d is a full frame camera so it would have an edge over the 7000/7100 in low light performance, but they are also about twice your current budget - they run around $1800 for just the body. So if it were me, I'd take a serious look at switching over to Nikon, either that or keep the T3i you currently have until you can afford to purchase the 6D.
Oh, also if your budget is a little flexible, the Nikon d600 would be a good one to give serious consideration too - it is full frame so the lowlight performance would be a big step up from where you are currently, it would give you better image quality than even a 6d can obtain, and a refurbished unit for the body only would run you around $1400 from
adorama. I know that's a little more than what your looking to spend but I put it out there for your consideration.
Hope that helps.