The original question raised by my initial post was associated with the exif data imbedded in the pic stating that the FL was 750 and Reza questioned whether that was correct. Nothing about file size... and I think that Reza in his later post was speaking about FOV being "larger" or appearing "closer". At least that's how I took it.
The topic of which format, FX or DX is better for the D800 has been discussed here, and virtually all who understand what "reach" really is, agree that you can crop before or after but it is either in camera or in PP. There are advantages to FX over DX and actually some for DX over FX including the ones you mention... but the bottom line is that cropping is cropping as you state.
Reza was questioning the 750mm FL that I stated for the pics..and I was explaining how it was calculated in the exif data, being "focal length of 300mm X 1.7 for the TC X 1.5 for the DX effect. That actually calculates to 765 but I can't explain for certain the 15mm difference.
Dan (Nikon D800,V2,Sony HX400V,Lumix ZS40) "I don't read, I just look at pictures" - Andy Warhol