For the price of a new 5DII you can buy a used 5D and maybe 70-200 f/2.8L to replace your 70-300. Don't forget, a fullframe like 5D (I or II) is quite a demanding camera (esp the 21 mp on 5DII), you really need good lens to go with it if you want the quality it can offer. If you buy 5DII, it...