There is a tool called GenX that will transfer Victoria 4/Michael 4 and Genesis characters to Genesis 2, and there is no visual difference from the result, but you get all of the benefits of the new Genesis 2 meshes. Also, I have found that most of the Victoria 4 / Genesis content (poses, clothing, skin textures etc) works on the Genesis 2 figure. Geo-grafted items such as genitalia designed for V4/V5 don't work with V6, but there are a couple of good V6 Genitalia out there. You have to pay for them, but I find that the Poison morphs for the Daz V6 genitals are really nice, along with Poison's AnusGen2. Also for variety 3feetwolf has a nice NewGenitalia for V6 which combined with morphs from 3xo give a nice result as well. All is available on renderotica.com.
There may be some free genitalia out there, but I found that the above options are really nice because they include overlays that add genital textures to any skin along with multiple uv maps. Once you have the genitalia, there is a lot of free content available that's mentioned elsewhere in the thread and forum. The key is that everything else made for V4 and Genesis/V5 works with Genesis2 / V6. Most poses need some minor adjustments to the shape, but that's usually the case anyway if you're using custom shapes. Some V4 skin textures simply need to be applied to a V4 figure, then re-saved into .duf format first, then they can be applied to the Genesis2 figure. Some v4 clothing will lose the breast bridge on conversion and be like shrinkwrap around the breasts, but a quick set of D-Forms can fix that within 5-10 minutes, and then they can be baked to morphs so that you only have to do it once per item.
In summary. I use Gen2/V6 models, converted my characters and have never looked back. After a bit of a learning curve about converting V4 and Gen items effectively, V6 can do everything V4 & V5 do, and it does it better.
But that's just my opinion.

Wolfschadowe