I do a lot of portraits, and I use DS and Poser, and a myriad selection of figures from Michelle, to Dusk, to V4, to Roxie, to Genesis 2 HD. I'm just going to offer my opinion, however.

As far as I'm concerned, the most realistic figures on the market are Genesis 2 model varieties. Not the base, but the base figure addons (Victoria 6, Olympia 6, Lee 6, etc -- and especially the $30 HD morphs for each figure), Proportions can be changed, but you may need to buy scaling add-ons for that. Also, you'll need morph packs to change the shapes and faces. Yes, you can spend a lot of money making the figures look truly realistic, but at least it can be done. Short of modelling in Zbrush yourself, none of the Poser figures will come as close (when it comes to muscle definition, bony protrusions, and skin fold and flesh shape details AND versatility). Just look at the promos. WYSIWYG.

You'll spend just as much getting Victoria 4 up to speed and the result won't be as good. As far as I know, there are no morphs that make the Poser native figures even come close to the level of realism, with the exception of Anastasia and Tyler. But while they are very good indeed, they also lack a lot of the versatility that Genesis 2 has, especially in the face and expressions. 

Genesis 2 works well enough in 64 bit Poser to render a single figure, easily. However, if I'm not mistaken, Poser 10 is only 32 bit.... so probably not so good.

Out of the box, Poser has a much better renderer than Daz Studio -- IMO -- thanks to IDL. However, if you're not concerned with having beautiful lighting for final render and just need the shadows in the right place because you're going to sketch or paint the render, then Daz Studio will work just fine for you.

What you'll primary be missing in DS is dynamic clothing. I find dynamic clothing to be essential for non-nude portraits because almost all the conforming clothing -- except the stuff of the finest quality (and usually highest price) -- looks, well, not very real to me. Fantasy clothing tends to perform better, but I may just think that because I don't see people wearing armor every day. :D However, if you can live with the look of conforming clothing, again, DS will be just fine.

My advice would be for you to install Genesis and the DSON importer so that you can see how it performs in Poser. If it's not to your satisfaction, then I'd go with DS without much further thought. (And I say this as a Poser user who only uses DS when I HAVE to). So, no agenda here. Just my opinion based on my personal experience. :)

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PoserPro 2014, PS CS5.5 Ext, Nikon D300. Win 8, i7-4770 @ 3.4 GHz, AMD Radeon 8570, 12 GB RAM.