Help needed please Imac 21"vs MacbookPro

Hi,

im really in trouble and dont know what to do...

I got a Imac27" at home and an macbook (the las of the white ones) and ive got an D600 and D800 and on the Imac27 with 12Gb Ram (i did upgrade) im very fine, and on the laptope its a no no (4GB ram)....

No to my issue, ive opened a Photostudio and i need a MAC and dont know which one to buy,to get an MACBOOKPRO and a big screen to work on (not sure if to go for the 13" or 15" eighter) or an 21" IMAC, bare in mind that my laptop is about to die, and my main isues are, is 8GB of RAM enough?Everyody is winding abuot the intelHD4000 NOT dedicated grafic chip from the macbooks (not sure if its in all of them) is it that mutch of a trouble, i just need it for Photoshop and photo edeting....

Any thought would be apreciated (sorry for my bad english im from spain)

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My flickr: http://www.flickr.com/photos/_gman_/