Technical comparison: MBP 15" mid-2010 or MBP 13" 2012 I plan to use the MBP to edit a lot of pictures. 

I am torn between spending less than $600 on a mid-2010 MBP 15" (Core i7 2.66Ghz) or a 2012 MBP 13" (Core i5 2.5Ghz) for less than $800. 

The MBP 15" tech is too old and it doesn't even have a USB 3.0 port but has a fast processor while the MBP 13" screen is too small for editing pictures (but I can attach it to an external monitor, no problem there). 

Should I just wait and save up for the MBP 13" or buy the MBP 15" now?

Can someone share they experiences and advice including the Graphics performances?
Let me provide you with my opinion:


The CPU can not be changed (well it could but at about $1000)
The slower USB is normally not a issue unless you are high user of external disks, etc. (and even then it is unlikely to make a noticeable difference)
Buying an external screen will always be an option regardless of model (only budget question).
Portability? Do you have to travel a lot?


Since your main use is to edit pictures, how about a graphics quality comparison?




  MacBook Pro (15-inch, Mid 2010)
  
  Graphics and video support
  
  
  NVIDIA GeForce GT 330M graphics processor with 256MB of GDDR3 memory on 2.4GHz and 2.53GHz configurations; or 512MB of GDDR3 memory on 2.66GHz configuration
  Intel HD Graphics with 256MB of DDR3 SDRAM shared with main memory
  Automatic graphics switching
  Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on an external display, both at millions of colors
  


Source: http://support.apple.com/kb/SP582

The Cons:
The MacBook Pro 15″ Mid 2010 had an 'intermittent black screen or loss of video' problem caused by the graphics card. The program has since ended.




  MacBook Pro (13-inch, Mid 2012)
  
  Graphics and video support
  
  
  Intel HD Graphics 4000
  Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on an external display, both at millions of colors
  


Source: http://support.apple.com/kb/SP649

Further details of the 13″ at NotebookCheck.net