For people interested in how to join two halves of an image, the easiest way is to render each half with an overlap and then open them in Photoshop. From there you can set up a canvas of the size you want (the size of the 100% render). paste the left image in and then the right image. Line both so they match up and then add a layer mask to the right image layer. Now you can paint away the hard line down the middle using the layer mask and black airbrush. (by painting black onto the layer mask, you make it transparent and able to see through to the layer below). This is very easy and takes about 10 mins if that to do.
Hopes this helps, Simon.