[Scarabsnap]

I currently use a Nikon D300 and my wildlife (mainly birds) lens is the 300mm f4 with a 1.4tc as required. Sometimes this simply isn't long enough and it's not always feasible to just get closer. As a result, some of my shots end up extremely cropped (eg about 900 x 900 pixels in a few cases). With this in mind, I've been looking at the Nikon V1 with FT1 adapter to effectively make 300mm reach 810mm on the V1's 2.7 crop factor as opposed to 450mm on the D300's 1.5 crop factor.

I don't want to start any 'crop' vs 'magnification' debates. All I want to know (or have a reliable formula for working out) is this: if one takes the extreme case referred to above as an example to work things out (900 pixels by 900 pixels on a DX sensor), which will give me the larger number of pixels on a bird (or better picture) - 300mm f4 and 10mp Nikon V1 with FT1 adapter or same lens on the 36mp Nikon D800 and just crop more?

I tried working it out, but just wasn't convinced I was approaching the maths correctly. I've read a couple of times that the D800 would have to be 75mp instead of 36 to match the effect of using the V1 and FT1, but there was no explanation of how this conclusion was reached.

Spending £4 - 5,000 or more on a longer lens is not an option for me. If I bought a D800, it would be MAINLY for landscape work with wide angle lenses rather than wildlife with tele lenses and it would obviously be more expensive than the V1 and FT1 approach, especially since I would immediately need to add at least a FF wide angle lens. The V1 approach also gives me a 'two birds with one stone' solution as I would get a compact system out of it as well. I realise I would lose C-AF when using the FT1. That's a nuisance, but not enough on its own to make the decision for me. I have considered all of this, and much more, but really just want to know the objective and measurable answer to my question about V1 and FT1 vs D800 and crop to get the picture without the final version being cut down to a tiny crop that equates to a 100% view in Lightroom.

Thanks in advance to anyone better equipped with maths skills and knowledge of pixel density vs crop factor, etc, who can answer this for me.