Upload & Sell: Off
If its in good condition, I think a 5D with 20k for $480 is an excellent deal. I had this same dilemma when I was shooting with a 60D and I chose the 5D. The 5D is slower (older processor, fps, handling, etc), but I certainly enjoy the photos that come out of it. FF is very nice and I think it'll be hard for me to go back to APS-C other than for the really small bodies like the NEX or the OMD lines.
Again, though, T3i with lenses will probably be a bit lighter/smaller package. Also, it has newer technologies, swiveling screen, liveview, on board flash, higher fps, higher max iso (for web-sized and small prints, I went all the way up to 6400 ISO), 18 MP sensor, larger/better LCD (higher resolution, I do miss this), the list goes on. Finally, the only real advantage of the 5D is that sweet sweet 12 MP full frame sensor; that comes with cleaner high ISO (maxing out at 1600), shorter (more control) DoF, focal lengths at actual focal lengths.
The 5D is 7 years old technology, while the T3i is only about a year old. If you go the 5D route, I'd check to see if the mirror has been reinforced. This isn't really an issue for me personally, as people have put it back and Canon fixes for free (with free cleaning and they used to even replace the shutter, but I think they've gone stingy over the years). You can't reliably check the shutter count on a 5D either, all the online checkers need DigicIII+, so I hope this person is someone you can trust or use your best judgement. Finally, if the first serial is 0 it was made in 2005, 1 = 2006, 2 = 2007, 3 = 2008. Good luck in your decision!
Edit- HAHAHA I took so long in typing my reply, there are many others now. I just want to add that I did love the two kit lenses (18-55 IS and 55-250 IS). They are quite sharp even if they are variable aperture.
On your question, I believe $600 will get a 5D sold right away, things have slowed down a little with the economy and all the new FF bodies that came out recently.
Edited on Oct 23, 2012 at 03:51 PM · View previous versions